L2 Students' metacognitive awareness of reading strategies and its relationship to reading comprehension

L2 Students' Metacognitive Awareness of Reading Strategies and its Relationship to Reading Comprehension Ana Cristina Lahuerta Universidad de Oviedo The present paper investigates students of English as a foreign language's metacognitive ability. Metacognitive ability refers to the learners's knowledge about their own cognitive resources, and their control of that knowledge in the learning situation. That knowledge will help them meet the demands of a learning situation more effectively and to take preventive actions to anticipate or recover from problems. We concéntrate on silent reading and undertake a study to investígate the metacognitive awareness of foreign language readers about their perceived ability to read in English and about the strategies they consider effective and focus on to read effectively in their foreign language (English), and its relationship to their reading comprehension performance. We think that reading comprehension can be improved if teachers learn about their subjects' beliefs and expectations about language learning in general and about strategies for reading in a foreign language in particular. 1. Introduction The purpose of this paper is to investígate metacognitive awareness of reading strategies. We carry out an analysis of non-native students' ideas about using certain strategies and about their potential effectiveness. Two main reasons justify this work. First, we know very little about metacognitive factors in second language reading. At the same time research has found that Icnowing about the nature of reading and about one's reading strategies will help inefficient readers to become better readers. A large body of research in second language reading has focused on readers' strategies. Researchers like Grellet (1981), Omaggio (1984), Hosenfeld et al. (1981), Loew (1984) defend the benefits for L2 students' reading of being taught reading strategies. Several empirical investigations have been conducted into reading strategies and their relationships to successful and unsuccessful second language reading (Hosenfeld, 1977; Haupman, 1979; Devine, 1984; Knight, Padrón and Waxman, 1985; Block, 1986; Sarig, 1987). These strategies include skimming and scanning, contextual guessing, reading for meaning, making inferences, predicting, previewing, anticipation, and more recently recognised strategies such as building and activating appropriate background knowledge and recognising text structure. Revista de Lenguas para Fines Específicos N"" 5 y 6 (1998-1999) 109 Ana Cristina Lahuerta Metacognitive knowledge refers to the general assumptions that students hold about themselves as learners, about factors influencing language learning and about the nature of language learning and teaching. Only recently has metacognitive knowledge begun to receive attention in second language research. A number of these studies have pointed out that the way in which learners perceive language learning may have a significant impact on their learning outcomes (e.g. Reid and Hresko, 1982; Weinert and Kluwe, 1987). According to these findings, successful learners develop insightful beliefs about language learning processes, their own abilities and the use of effective strategies that may compénsate for possible weaknesses. This, in turn, has a facilitating effect on students' learning, for they see themselves as initiators of their own learning and it helps them to rely on their own potential as good language learners. Needless to say, these students tend to develop a more active, and thus, autonomous attitude that allows them to take charge of their learning whatever the situation may be. Some research has begun to focus on students' awareness of reading strategies. Relevant research on metacognitive strategy training has been conducted in second language reading by Carrell, (1985, 1989b), Padrón, (1985), O'Malley, (1987), Sarig and Folman, (1987), on the assumption that, as we said before, knowing about the nature of reading and about one's reading strategies will help inefficient readers to become better readers. Thus if a reader is aware of what is needed to perform effectively, then it is possible to take steps to meet the demands of a reading situation more effectively. If, however, the reader is not aware of his or her own limitations as a reader or of the complexity of the task at hand, then the reader can hardly be expected to take preventive actions to anticipate or recover from problems. A series of studies investígate the relationships between perceptions about strategies, strategy use and reading comprehension (Waxman and Padrón, 1987; Padrón and Waxman, 1988; Barnett, 1988; Carrell 1989a). lio Revista de Lenguas para Fines Específicos N°'' 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and üs Relationship.. Carrell's (1989a) study focuses the metacognitive awareness of second language readers about reading strategies in both their first and second language, and investigates the relationship between their metacognitive awareness and their comprehension in both first and second language reading. She observed a significant relationship between metacognitive awareness about reading strategies and reading performance. Thus, the subjects' preference for global or local strategies had an effect on reading performance. Global strategies have to do with use of background knowledge, reading for the text gist and use of textual organization, whereas local strategies are those relating to sound-letter, word-meaning and sentence syntax. In Carrell's study this preference varied according to whether the subjects were reading in a first or in a second language. For reading in the first language, readers tended to prefer global strategies and local reading strategies tended to be negatively correlated with reading performance. For reading in a second or foreign language, the Spanish Ll group reading in English as a second language (ESL), of more advanced proficiency levéis, tended to be more global in their perceptions of effective and difficulty-causing reading strategies and for this group some global reading strategies were positively correlated with reading performance, whereas the English Ll group reading in Spanish as a foreign language (EFL), at lower proficiency levéis tended to be more local in their perceptions of effective strategies. Some of the local and difficulty-causing reading strategies were positively correlated with reading performance. 2. Our research study Our study continúes the analysis of metacognitive perceptions of non-native readers about reading strategies and the influence these perceptions or ideas may have on second language reading performance. As we have said before, students carry beliefs about their weaknesses and strengths and their self-concept as learners, and they also Revista de Lenguas para Fines Específicos N°* 5 y 6 (1998 y 1999) 111 Ana Cristina Lahuerta develop some ideas about using certain strategies and about their potential effectiveness. This paper undertakes an analysis of these beliefs and ideas in students of English as a foreign language. We carry out a descriptive study about students' perceived ability to read in English and about the strategies they consider effective and focus on to read effectively. We also carry out an empirical study about the relationship between our students' judgments about the effectiveness of the various reading strategies and the effectiveness of their reading. We hypothesize that different results to those in Carrell's study might emerge from a similar study but with different kinds of subjects. The subjects of our study are all students of English as a foreign language, at a low proficiency level in English. As this is the profile of the students we usually wotk with we hope that the results we obtain will contribute to improving both our knowledge of our students and our teaching. 3. Metacognitive questionnaire A questionnaire was used to elicit relevant Information about the subjects' ideas about their own reading and their judgments about silent reading strategies. It consists of three groups of statements. The first group of statements is related to the subjects' perceived reading ability in the target language. It includes the techniques and resources which characterize a good reading behaviour, as they appear in the literature (Grellet, 1981; Nuttall, 1996; Silberstein, 1994). This first group consists of six statements which enquire about the faculty of predicting or guessing what is to come next in the text, about anticipation or the ability to use prior knowledge and experience to understand the content of the text, about whether subjects recognize the organization of the text, distinguishing between main points and supporting details, and relating Information which comes next in the text to previous Information in the text, about whether subjects are able to assess and evalúate the text, being aware of the 112 Revista de Lenguas para Fines Específicos N°» 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and üs Relationship... writer's intention, of his point of view and possible bias, and about whether they have a good sense of when they understand something or not. The next group of statements tries to reveal the reader's resources to face problems duríng reading and solve them satisfactorily. They are five statements pertaining to what subjects do when they do not understand something, whether they use some repair strategies or give up and stop reading. The rest of the questionnaire consists of seventeen statements about what the subjects do to read effectively and about reading behaviours of good readers. Within these categories individual items focus on various types of reading strategies related to reading comprehension (Hosenfeld 1977; Brown 1980; Baker and Brown 1984; Devine 1984; Block 1986; Bartnett 1988): 1) phonetic, pronunciation, or sound-letter aspects of decoding; 2) word-level aspects of meaning; 3) sentence, syntactic decoding; 4) details of text content; 5) global aspects of textual meaning, or text gist; 6) background knowledge; and 7) textual organization. These three groups of statements are taken from Carrell's (1989a) questionnaire. We thought that the Information they contain could provide complete and relevant Information about the subjects metacognitive conceptualizations about reading strategies. They cover reading techniques, repair strategies a reader uses when comprehension fails and the reading strategies related to comprehension suggested in the literature. Using a 1-5 Likert Scale (l=strongly agree, 5=strongly disagree), subjects judged twenty-eight statements about silent reading strategies in English. In order not to have level of language proficiency in the second language affect results on the metacognitive questionnaires, subjects received the questionnaire in their native language (see questionnaire in Appendix I). Revista de Lenguas para Fines Específicos N™ 5 y 6 (1998 y 1999) 113 Ana Cristina Lahuerta 4. Subjects. A group of eighty-eight native speakers of Spanish participated in the study. These subjects were studying at the Technical University School of Industrial Engineering in Gijón. They were of lew proficiency level in English. 5. Procedures. Subjects read a text in English and answered six comprehension questions about the text (cf. Appendix II), then responded to the metacognitive questionnaire about reading in that language. The text was on the topic of corrosión, with a problem/solution type of rhetorical organization. The text was an excerpt from an article by P. Tweedale entitled «Beating the fire risk with water based hydraulics» from the journal Professional Engineering. This is typical of the material the informants were regularly required to read throughout their courses. 6. Results Descriptive and correlational statistics based on the response data were obtained using the statistical program SPSS for Windows 6.0. 6.1. Descriptive analysis We will start analysing each variable separately. Within the ability Ítem group, the first six statements in the questionnaire, a high proportion of the subjects agreed with statements 2, 3, 5 and 6 (mean values= 2.5; 2.419; 2.126; 1.437 respectively). Thus, 53.4% of the subjects agreed with the statement that when reading silently in English, they were able to anticípate the difference between main points and supporting details whereas 11.6% of the subjects disagreed with this statement; a high proportion of subjects (61.7%) agreed with the statement that when reading silently in English, they were able to relate Information which comes next in the text to previous Information in the text, and only 7% disagreed with 114 Revista de Lenguas para Fines Específicos N"'' 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and üs Relationship... this statement. A large number of subjects (74.7%, of which 52.9 agreed and 21.8 strongly agreed) said that they were able to use their prior knowledge and experience to understand the contení of the text they were reading, and 95.4% of the subjects stated that they had a good sense of when they understood something and when they did not (of these 62.1% strongly agreed with this reading ability). With respect to statement 4 (when reading silently in English I am able to question the significance or truthfulness of what the authors says), 43% of the subjects showed an neutral attitude towards this ability, although more agreed (36.1%) than disagreed (20.9%) with it, the mean valué was 2.779. Finally, 40.7% of the subjects disagreed and 11.6 strongly disagreed with the statement that when reading silently in English, they were able to anticípate what would come next in the text (mean vaIue=3.512). With respect to repair strategies or what they do when they do not understand something (statements 7 to 11 in the questionnaire), a large proportion of subjects (80.4%) said that when they did not understand something, they kept on reading hoping for clarification further on (mean valué 2.034); 71.2% said that they reread the problematic part (mean value=2.184); 66.3% went back to a point before the problematic part and reread from there (mean value=2.337); 60.4% affirmed that they looked up unknown words in the dictionary (mean value=2.337). Finally, 52.3% strongly disagreed and 31.4 disagreed with the statement that when they did not understand something they gave up and stopped reading (mean value=4.279). With respect to the strategies that our students tended to focus on in order to read more effectively (statements 12 to 20), 94.1% of the subjects tended to focus on getting the overall meaning of the text (52.4% of the subjects strongly agreed and 41.7% agreed with this statement; mean value=1.560), 60.7% tended to focus on relating the text to what they already know about the topic (mean vaRevista de Lenguas para Fines Específicos N™ 5 y 6 (1998 y 1999) 115 Ana Cristina Lahuerta lue=2.429), 59.8% tended to focus on understanding the meaning of each word (mean value=2.378), and 47% tended to focus on looking up words in the dictionary (mean value=2.578). On the other hand, the subjects did not focus to read effectively on mentally sounding out parts of the text (37.8% disagreed and 31.7 strongly disagreed with this statement; mean value=3.915) and being able to pronounce each whole word (34.9% strongly disagreed and 31.3 disagreed with this statement; mean value=4.253). They showed a neutral or intermedíate level of agreement with the strategies of using the organization of the text, the grammatical structures, and focusing on the details of the content to read effectively (42.2%, 41% and 46.4% of the subjects respectively neither agreed ñor disagreed with these strategies; mean value=3.084, 3 and 3.083 respectively). That is, the subjects tended to focus in order to read more effectively on two strategies that refer to global aspects of textual meaning and background knowledge, and on two local strategies, understanding the meaning of each word and looking up words in the dictionary. In the case of what are perceived to be effective strategies characteristic of the reading behaviours of the best readers subjects know (statements 21 to 28), these are, in order of preference: understanding the overall meaning of the text (62.7% strongly agreed and 28.9 agreed that this strategy was effective; mean value= 1.494), guessing at word meanings (39% strongly agreed and 29.3 agreed with this statement; mean value=2.098), integrating the information in the text with what he/she already knows (66.3% agreed that this strategy was effective; mean value=2.205), recognizing words (64.6% agreed that this strategy was effective; mean value=2.293), grasping the organization of the text (61% agreed with this statement; mean value=2.207), focusing on the details of the content (45.8% agreed with this statement; mean value=2.651), and sounding out words (39.8% agreed with this statement; mean value=2.964). 116 Revista de Lenguas para Fines Específicos N°^ 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and its Relationship.. jects in the first cluster are 43, 21 in the second and 16 in the third. The number and proportion of subjects in each cluster appears in Table 4: Subjects Percentage LOCAL HIGH 16 20 LOCAL LOW 43 53.7 GLOBAL 21 26.25 TABLE 4: Cluster of subjects according to their local/global tendency in group B of statements. Now we will show the profiles of each of the clusters. These are obtained taking as the basis the result of the cluster analysis and calculating the mean valué of the results obtained by the individuáis in each cluster. In the group of statements on the strategies subjects focused on to read more effectively, we have seen that the three clusters show a tendency towards local strategies. In cluster 1 (low tendency to local strategies), the mean score on the reading comprehension test is 4.67 (out of a maximun of 6). In cluster 2 (high tendency to local strategies) the mean is 4.76 and in cluster 3 (intermediate tendency to local strategies) the mean is 5.15. The highest mean score is in the group of subjects with an intermediate tendency to local strategies. In the group of statements on what subjects judged as effective reading behaviours, clusters 1 and 3 showed a tendency to local strategies. The mean score in these clusters is 4.85 and 4.76 respectively. In cluster 2, which shows a tendency to global strategies the mean score on the comprehension test is 5.09. As we can see, the mean scores on the reading comprehension test are similar in the clusters. We can confirm that the preference for global or local strategies does not have a significant influence on comprehension. Revista de Lenguas para Fines Específicos N°" 5 y 6 (1998 y 1999) 123 Ana Cristina Lahuerta 7. Conclusión We have carried out a descriptive study to investígate our readers' perceived ability to read in English and their judgments about the efficiency of the various reading strategies. Regarding this question, the foUowing results are noteworthy: Subjects see themselves as able to use prior knowledge and experience to understand the content of the text, able to recognise the organization of the text, to assess and evalúate the text and capable of knowing when they understand something and when they do not. They see themselves as resourceful readers who in the face of reading difficulties use strategies to clarify the meaning instead of giving up and stop reading. Subjects tended to focus on in order to read more effectively, and tended to judge as effective strategies two strategies that refer to global aspects of textual meaning and background knowledge, and two local strategies, understanding the meaning of each word and looking up words in the dictionary. We also carried out an empirical study about the relationship between the readers' ideas and judgments about the effectiveness of strategies and their reading performance. We did not find a significant correlation between the students' ideas about strategies and their potential effectiveness, and their reading comprehension performance. When we analysed the general tendency to global or local strategies subjects tended to focus on local strategies to read more effectively, and tended to judge local strategies as effective. When we analysed the tendency to global or local strategies more specifically within the students using a cluster analysis, the same tendency towards local strategies was found. This result coincides with Carrell's (1989) a study where the Spanish-as-a-foreign-language group tended to be more local in their perceptions of effective reading strategies. 124 Revista de Lenguas para Fines Específicos N« 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and its Relationship... However, unlike Carrell's study, the results obtained in the comprehension test were not influenced by the students' preference for global or local strategies. We think that there are several reasons for the absence of significant correlation between the students' metacognitive knowledge about strategies and their comprehension performance. One is that the reading comprehension test may have not been difficult enough to be relevant of the level of comprehension of the students, because, as we saw, most of the subjects understood the text and when we analysed the profile of each of the clusters, we observed that the mean scores on the reading comprehension test were similar in the clusters. Related to this is the belief that a reading comprehension test may not be enough to measure the subjects' reading performance and the relationship between awareness of reading strategies and reading performance must be studied on a wider variety of reading , tasks. We observe a general preference for local strategies, corroborated in the more specific cluster analysis. This preference may be explained by the fact that our students have confusing ideas about themselves as learners, that they know very little about different strategies and about their potential effectiveness. One of the most important practical results of our study is the Information it offers about foreign language students' awareness of reading and reading strategies. This Information is especially important in our attempt to help our students in their learning, so that they become autonomous learners able to identify needs and set objectives in accordance with their goals, and able to evalúate and monitor their progress over time. The next step is to help them learn about their learning styles and preferences and about their beliefs and expectations about language learning in general and about strategies for reading in a foreign language in particular. Revista de Lenguas para Fines Específicos N°-' 5 y 6 (1998 y 1999) 125 Ana Cristina Lahuerta WORKS CITED Baker, L. and A.L. Brown. 1984. "Metacognitive Skills and Reading" in P.D. Pearson, ed. Handbook of Reading Research. New York: Longman. Barnett, M.A. 1988. "Reading through context: How real and perceived strategy use affects L2 comprehension" in The Modern Language Journal 72: 150-161. Bisquerra, R. 1987. Introducción Conceptual al Análisis Multivariable. Tomo I, PPU. Block, E. 1986. "The comprehension strategies of second language readers" in TESOL Quaterly 20: 463-494. Brown, A.L. 1980. "Metacognitive Development and Reading" in Spiro, R.J., B.C. Bruce and W.F. Brewer, eds. Theoretical Issues in Reading Comprehension, Hillsdale, NJ: Erlbaum. Carrell, P. L. 1985. "Facilitating ESL reading by teaching text structure" in TESOL Quaterly 19: 727-752. Carrell, P.L. 1989a. "Metacognitive awareness and second language reading'. The Modern Language Journal 73: 121-131. Carrell, P. L. 1989b. Scoring System for Open-Ended Questions and Open-Ended Semantic Map. Unpubüshed Manuscript. Southern Illinois University, Carbonéale. Devine, J. 1984. "ESL Readers' Internalized Models of the Reading Process" in J. Handscombe, R. Orem and B. Taylor, eds. On TESOL '83. Washington:TESOL. Gambrell, L.B. and B.S. Heathington. 1981. "Adult Disabled Readers' Metacognitive Awareness about Reading Tasks and Strategies" in Journal of Reading Behavior 13: 215-222. Garner, R. 1987. Metacognition and Reading Comprehension. Norwood, NJ: Ablex. Grellett, F. 1981. Developing Reading Skills: A Practical Guide to Reading Comprehension Exercises. Cambridge: Cambridge University Press. Haupman, P.C. 1979. "A comparison of first and second language reading strategies among English-speaking university students" in ¡nterlanguage Studies Bulletin 4: 173-201. Hosenfeld, C. 1977. "A preliminary investigation of the reading strategies of successful and not successful learners" in System 5: 110-123. Hosenfeld, C, V. Arnold, J. Kirchofer, J. Laciura and L. Wilson. 1981. "Second language reading: A curricular sequence for teaching reading strategies" in Foreign Language Annals 14: 415-422. 126 Revista de Lenguas para Fines Específicos N™ 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and its Relationship.. Knight, S.L., Y.N. Padrón and H.C. Waxman. 1985. "The cognitive reading strategies of ESL students" in TESOL Quaterly 19: 789-792. Loew, H.Z. 1984. "Developing strategic reading skills" in Foreign Language Annals 17: 301-303. Nuttall, C. 1996. Teaching Reading Skills in a Foreign Language. Oxford: Heinemann. O'Maggio, A.C. 1984. "Making Reading Comprehensible" in Foreign Language Annals 17: 305-308. O'Malley, J.M. 1987. "The effects of training in the use of learning strategies on learning English as a second language". In Wenden, A. and J. Rubin, eds. Learner Strategies in Language Learning. Englewood Cliffs, N.J.: Prentice Hall. Padrón, Y.N. 1985. Utilizing Cognitive Reading Strategies to Improve English Reading Comprehension of Spanish-Speaking Bilingual Students. Unpublished doctoral dissertation, University of Houston. Padrón, Y.N. and H.C. Waxman. 1988. "The effect of ESL students' perceptions of their cognitive strategies on reading achievement" in TESOL Quaterly 22: 146-150. París, S.G. and M. Myers. 1981. "Comprehension Monitoring, Memory, and Study Strategies of Good and Poor Readers" in Journal of Reading Behaviour 13: 5-22. Punj, G. and D.W. Stewart, 1983. "Cluster analysis in marketing research: review and suggestions for application" in Journal of Marketing Research XX: 134-148. Reid, D.K. and W.P. Hresko. (eds.). 1982. Metacognition and Learning disabiíities. Oxford: Oxford University Press. Ruiz Vega, A.V. 1993. Segmentación del Mercado Financiero al por Menor en Asturias, Doctoral Dissertation, University of Oviedo. Sarig, G. 1987. "High-level reading in the first and in the foreign language: some comparative process data" in J. Devine, P.L. Carrell and D.E. Eskey, eds. Research in Reading in English as a Second language. Washington, D.C.: TESOL. Sarig, G. and S. Folman 1987. "Metacognitive awareness and theoretical knowledge in coherence production". Paper, Communication and Cognition International Congress, Ghent. Silberstein, S. 1994. Techniques and Resources in Teaching Reading. Oxford: Oxford University Press. Revista de Lenguas para Fines Específicos N'" 5 y 6 (1998 y 1999) 127 Ana Cristina Lahuerta Waxnian, H.C. and Y.N. Padrón. 1987. "The Effect of ESL Students' Perceptions of their Cognitive Strategies on Reading Achievement". Paper presented at the Annual meeting of the Southwest Eduactional Research association, Dallas, TX. Weinert, F.E. and R.H. Kluwe. (eds.) 1987. Metacognition, Motivation and Understanding. London: Lawrence Erlbaum Associates. APPENDIX I METACOGNITIVE QUESTIONNAIRE The following statements are about silent reading in English. Picase indícate the level of your agreement or disagreement with each statement by circling the appropriate number: 1 indicates strong agreement, 5 indicates strong disagreement. 1. When reading silently in English, I am able to anticípate what will come next in the text 2. When reading silently in English, I am able to recognize the difference between main points and supporting details 3. When reading silently in English, I am able to relate information which comes next in the text to previous information in the text 4. When reading silently in English, I am able to question the significance or truthfulness of what the author says 5. When reading silently in English, I am able to use my prior knowledge and experience to understand the content of the text I am reading 6. When reading silently in English, I have a good sense of when I understand something and when I do not When reading silently in English, if I don't understand something, 7. I keep on reading and hope for clarification further on 8. I reread the problematic part 9. 1 go back to a point before the problematic part and reread from there. 10. I look up unknown words in a dictionary 11. I give up and stop reading When reading silently in English, the things I do to read effectively are to focus on: 12. mentally sounding out parts of the words 13. understanding the meaning of each word 128 Revista de Lenguas para Fines Específicos N"" 5 y 6 (1998 y 1999) L2 Students' Metacognitive Awareness of Reading Strategies and its Relationship... 14. getting the overall meaning of the text 15. being able to pronounce each whole word 16. the grammatical structures 17. relating the text to what I already know about the topic 18. looking up words in the dictionary 19. the details of the contení 20. the organization of the text The best reader I know in Enghsh is a good reader because of his/her ability to 21. recognize words 22. sound out words 23. understand the overall meaning of a text 24. use a dictionary 25. guess at word meanings 26. intégrate the information in the text with what he/she already knows 27. focus on the details of the content 28. grasp the organization of the text APPENDIX II TEXT WATER-BASED HYDRAULICS Hydraulic power was first based on water. The development of the oil industry meant the ready availability of power transmission fluids with improved characteristics compared to water. Oil has better lubrication ability and increased viscosity which allowed much higher contact loads to be achieved in the machinery as well as lower leakage rates. Water-containing hydraulic fluids have evolved since the late 1940s in response to the fire ignition risks of oil systems. The safety concerns of the steel, mining, and offshore users have played a major part here. Initially, these fluids were 40/60 water/oil mixture but these have been progressively modified into the 95/5 systems available today. High water-based fluids have to contain additives so that internal components relying on metal upon metal contact can opérate without excessive wear. Water-powered machinery with its inherently non-polluting media is a very attractive prospect especially because of environmental concerns about the conRevista de Lenguas para Fines Específicos N"" 5 y 6 (1998 y 1999) 129 Ana Cristina Lahuerta sequences of oil leakages and the disposal of oil residues. In order to engineer effectively for water power, the foUowing points need to be considered: — Water lacks boundary lubrication. When oil is used as a hydraulic fluid, it provides lubrication and reduces corrosión. Machinery can opérate with some rubbing contact without excessive wear. When water is used, component surfaces in sliding contact should be made of corrosion-resistant non-metallic materials such as ceramics or polymers. — Water has low viscosity. Sealing is more difficult. — Corrosión. Metals are significantly affected by water. The use of corrosión preventing additives or non-corrosive materials is advised. — Contamination. Using 'raw water' such as sea-water which contains significant amounts of particles and salinity can cause wear and corrosión. Filtration may be necessary. P. Tweedale «Beating the fire risk with Water Based Hydraulics», Professional Engineering. COMPREHENSION QUESTIONS 1. Why is oil superior to water as a hydraulic fluid? 2. Why were water-containing fluids developed? 3. How can the wear of metal parts be reduced in water-based hydraulic equipment? 4. What materials should be used where possible for component surfaces in sliding contact? 5. Why is sealing difficult with water-containing fluids? 6. Why is filtration of sea-water advised? 130 Revista de Ler\guas para Fines Específicos N°' 5 y 6 (1998 y 1999)