NATURE 



361 



THURSDAY, FEBRUARY 16, 1893. 



QUALITATIVE CHEMICAL ANALYSIS. 

 Qualitative Analysis Tables and the Reactions of certain 

 Organic Substances. By E. A. Letts, D.Sc, Ph.D., 

 F.R.S.E., F.C.S., &c. (Belfast: Mayne and Boyd, 

 1892.) 



THE author in his preface says, " Every teacher has 

 his own methods— acquired not only from his ex- 

 perience, but also largely through the researches of others 

 —and this book embodies mine." Therefore the volume 

 cannot fail to be welcome to those who take an interest 

 in the teaching of analytical chemistry. But it is sur- 

 prising to find that Prof. Letts has until quite recently 

 followed the old method of dictating reactions and 

 methods to his students, and allowing them to work from 

 their own notes. For the last fifteen years there has 

 been no lack of text-books of qualitative analysis, and 

 Prof. Letts has found, what probably all teachers of the 

 subject are aware of, that students rarely take accurate 

 notes. But, however exact they may be, every one knows 

 that manuscript is not so easily deciphered nor so readily 

 referred to as a printed page. 



The methods of work given are, of course, more or 

 less on the ordinary lines. The final test for bismuth de- 

 pends upon the production of its black suboxide, and this 

 reaction has much to recommend it, though probably many 

 would prefer the oxychloride reaction. The use of am- 

 monium molybdate as a separative reagent in qualitative 

 analysis we do not consider advisable for many reasons, 

 but no complaint can be lodged against it on the score of 

 its accuracy. 



There can be no doubt whatever that both Prof. Letts 

 and his students will find considerable advantage in the 

 use of boldly-printed statements of methods. But the 

 author begins his preface by stating that although the 

 book has been written chiefly for his own students, he 

 will be glad if it prove of service to others also. This 

 lays the volume open to general criticism, and prompts 

 us to complain that it is neither so clear nor so systematic 

 as it might have been. As to the want of clearness, there 

 are a few expressions that can easily be altered in a second 

 edition, and these we lay no particular stress upon. For 

 example, at page 27, in the description of Bunsen's dry 

 tests, we read : — " The charred end of the match is next 

 moistened with fused carbonate of soda." At page 40 it 

 states that the solution " is mixed with its own volume of 

 chloride of ammonium." One assumes this to be a solu- 

 tion, but if so the strength of it is not given, and we fear 

 that the bulk of the solution to which it is to be added 

 will be likely to vary enormously according^ to the pecu- 

 liarities of the student and the character of the substance 

 he is at work upon. 



The more important want of clearness maybe exempli- 

 fied by taking the case of a student who has Epsom salts 

 given to him as a simple salt. This can hardly be called 

 an out-of-the-way substance, but so far as we can 

 discover, the student in following these tables would 

 examine it by the following series of operations : Heat- 

 ing on platinum wire to see the colour of the flame. 

 NO. I 2 16, VOL. 47] 



Heating on a borax bead in the outer and inner flames. 

 Heating on a carbonate of soda bead. Heating on 

 charcoal (if a white mass resulted, which with cobalt 

 nitrate gave a " faint pink," the metal might be recog- 

 nised here, but as magnesium sulphate does not readily 

 yield this reaction in most cases the student would pass 

 on). Heating on charcoal with sodium carbonate. 

 Heating in a glass tube closed at one end. Repeat- 

 ing with bisulphate of potash. Repeating with black 

 flux. Repeating with magnesium wire. He would then 

 dissolve the substance in water, and test a part of the 

 solution for ammonia by heating it with caustic alkali. 

 Then heat a part on a platinum wire for the flame 

 colouration, a test that has already been done on the 

 solid, and then pass on to the examination of the solu- 

 tion in the ordinary way for the base, and finally search 

 for the acid if it is not already found. It may be taken 

 for granted that this fiddling about with the substance is 

 not intended, but the volume does not appear to contain 

 directions as to how to go more directly to work. 



The want of system that we complain of is acknow- 

 ledged by the author himself in picking out certain parts 

 and labelling them as " systematic." If the whole were 

 systematic this distinction would obviously be meaning- 

 less. As this fault exists in many of the text-books and 

 in much of the teaching that we have had experience of, 

 we are tempted to make a few general remarks upon the 

 matter without special reference to the volume under 

 notice. 



That qualitative analysis is often regarded as a 

 very unimportant branch of chemistry, may account 

 for its comparative neglect. One constantly meets with 

 students who are able to perform quantitative operations 

 of not too complex a character with commendable 

 accuracy, and that can with a little guidance do many 

 sorts of "research work," but are wholly unable to per- 

 form with certainty a qualitative analysis of a compara- 

 tively simple substance. They may happen to find most 

 or all of its constituents, but they have no confidence in 

 their result ; they do not feel sure that they have missed 

 nothing, or indeed that everything they have found is 

 unmistakably present, and generally they have little if 

 any idea of the degree of accuracy of their work. They 

 cannot distinguish between a principal constituent and 

 one that is present in a comparatively small proportion. 

 This incompetency must be ascribed very largely to the 

 fact that students are too often urged on to work that a 

 casual observer might regard as more important. The 

 foundation is neglected for the sake of the superstructure. 



But having regard only to that amount of practice in 

 qualitative work that still remains possible for the 

 average student, there is too often a lack of method that 

 is surprising if not disastrous. As a rule, it is con- 

 sidered desirable to get first an idea of the general 

 character of the substance given for examination 

 by a few dry tests, but these, as often done, are not only 

 of no use, but serve in a conspicuous manner to train the 

 student in the making of careless and imperfect observa- 

 tions, and in the dodging about from one operation to 

 another with no idea of the proper sequence or inter-depen- 

 dence of the various parts of the work. In the analytical 

 examination of even the simplest of substances, from the 



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