XVII SULPHUR AND ITS COMPOUNDS 253 EXPT. 262.-The flask which contained the copper and sulphuric acid should next be examined. It will be observed that most of the copper has disappeared, and the contents of the flask have a black colour. Add some water, shake well, and filter, when a blue liquid is obtained. Evaporate this partially, and put aside to crystallise. It will be found that blue crystals are so obtained. These crystals are what are known commercially as blue vitriol, the chemical name being sulphate of copper. We may therefore state that Copper and sulphuric acid produce sulphur dioxide and copper sulphate. Sulphur Trioxide and Sulphuric Acid.-Although sulphur dioxide does not burn, yet by suitable means we can make it combine with more oxygen and produce a higher oxide, which is known as sulphur trioxide. EXPT. 263.-In the tube AB place some platinised asbestos,1 and pass through the tube a well-dried mixture of sulphur dioxide and oxygen or air, the gases then being had into the cooled tube D. Heat the tube of asbestos, and note that white fumes are formed which condense in the cooler flask to form a white powder or crystals. This powder is sulphur trioxide, and we may now state :— Sulphur dioxide with oxygen forms sulphur trioxide. 1 This is prepared by dipping asbestos fibres into (1) platinic chloride solution, (2) ammonium chloride solution, and heating strongly. By this means the asbestos becomes coated with a quantity of very finely divided platinum. Now Ready. Fcap. 4to. Price 2s. 6d. AN EXERCISE BOOK OF ELEMENTARY PRACTICAL PHYSICS BY RICHARD A. GREGORY, F.R.A.S. London MACMILLAN AND CO., LIMITED NEW YORK: THE MACMILLAN COMPANY EXTRACT FROM PREFACE TEACHERS will find that young students of average mental ability are able to work through the exercises in this book from the simple measurements of length at the beginning to the more difficult experiments at the end. The object of practical work of this kind is to teach students to measure accurately, to manipulate carefully, to see fully, to reason intelligently, and to express their observations and results clearly. Almost the only information given in the book consists of instructions as to how the exercises and experiments are to be done; the student being left to find out and describe the results for himself. Though intended, in the first instance, for Organised Science Schools under the Science and Art Department, the exercises arranged in this book meet other prescribed courses. If the exercises illustrating the mechanical powers are omitted, the remainder_cover part I. of the Elementary Course of Practical Science for Evening Continuation Schools. With the same omission, the exercises cover the Experimental Arithmetic and Physics of the Alternative Courses for Class Subjects in Elementary Day Schools, from Standards I. to V. inclusive. The Regulations referring to this subject point out that "the instruction should be experimental, the experiments being carried out by the scholars." Another course which the exercises in a section of the book illustrate is that prescribed for the Third Stage of Mechanics as a Specific Subject in Elementary Day Schools. The Education Department expressly states that the instruction in Mechanics "should be purely descriptive and experimental"; and if provision can be made for the performance of the experiments by the pupils themselves, the best results will be obtained. But if not, teachers will find that by following the instructions laid down in this book, they can illustrate to their classes the chief mechanical principles with apparatus that need only cost a few shillings. The exercises in the first half of the book are of a very elementary character; they are introduced in order to give students a clear and definite knowledge of the metric system of weights and measures, and to give practice in the use of decimals. The Select Committee appointed by the House of Commons to inquire into the changes most desired in our cumbersome system of weights and measures recommended "That the metrical system of weights and measures be taught in all public elemen tary schools as a necessary and integral part of arithmetic, and that decimals be introduced at an earlier period of the school curriculum than is the case at present." The opening exercises in this book should help to carry out the Committee's recommendations. PRESS OPINIONS Educational Review.-"Will be found extremely useful to students in organised science schools under the Department of Science and Art, in evening continuation schools, and in the highest standards in elementary schools. So far as we have tested them, the exercises seem well selected and carefully graduated." Educational Times.-" Mr. Gregory is no mere intelligent dispenser of other men's prescriptions. His book is essentially original. He has one of the most valuable qualities in a teacher-a ready invention.” Saturday Review.-"In no book that we know of is this method (Froebel's) quite so ably set forth as in this admirable book of exercises that Mr. Gregory has arranged. . . . Here and there he shows himself not only a scientific teacher but a remarkably ingenious one. Guardian.-"The publishers have produced a thoroughly good half-crown exercise book which is a step forward in science teaching, especially where numbers, drill and time-tables are concomitants." Technical World.-With such a guide and the experience reaped whilst Mr. Gregory was assistant to Professor A. M. Worthington, F.R.S., at Clifton College, one naturally expected a really trustworthy work, and having carefully gone through the book, we unhesitatingly say that we are not disappointed. . . . In conclusion, we would heartily recommend this book to the notice of all science teachers, and believe, if judiciously used, cannot but produce good results." Scotsman." It is so novel, attractive, and practical that it will not only teach its subject, but give students a new interest in it." Chap. 1. Forms of Matter; 2. Measurement of Space, Mass, Weight, |