270 



NATURE 



\7an. 25, 



1877 



can combine with another in two different but definite 

 proportions by weight. The study of the hydrocarbons 

 and of carbon monoxide and dioxide was not talcen up 

 until two years later. (See Roscoe's "John Dalton and 

 his Atomic Theory," Science Lectures, 1874.) 



It has probably been from considerations of space that 

 Mr. Butler has been unable to do more than glance, in 

 the briefest possible manner, at the progress of modern 

 theory, and we fear that in one or two instances, his 

 reader may complain that in the effort to be concise he 

 has become obscure. The idea of the polyatomicity of 

 the elements is dismissed in a single line. The doctrine 

 of materia prima has played such an important part in 

 the past, and if we may judge from the signs of the times, 

 is destined to play a still more important part in the future, 

 that it is surely an omission of some moment to neglect 

 all mention of Front's hypothesis, of Dunias's extension of 

 it, of its unquestionable influence upon the French school, 

 and of the labours of Stas in connection with it. It is to 

 be regretted too that so little is said of the rise of what 

 may be termed the physical side of chemistry ; of, for 

 example, the influence of Dulong and Petit's law, of the 

 law of Avogadro, of Mitscherlich's law of isomorphism, 

 and that no direct reference is made to modern notions 

 of the constitution of matter. It is true that certain of 

 these matters are mentioned in subsequent sections of the 

 general article, but they have their proper place in a 

 historical account of the growth of the science. Lastly, 

 the value of this portion of the article would have been 

 greatly augmented by some reference to the bibliography 

 of chemical history ; Mr. Butler will excite the interest 

 and curiosity of many students by his well-written and 

 thoroughly readable sketch ; he would have increased 

 their gratitude by informing them how they might satisfy 

 their craving for further knowledge. 



The second, and by far the largest, portion of the 

 article (it occupies nearly two-thirds of the whole) treats 

 of Inorganic Chemistry, and is the work of Prof. Arm- 

 strong. In its main features it differs considerably from 

 the ordinary run of descriptive treatises, although we 

 question whether any one of them exhibits a more com- 

 plete coup d'csil of the present position of this branch of 

 the science. No space is wasted on mere technics (if we 

 may employ a word which is sanctioned by Worcester), 

 and it would be almost impossible for one ignorant of the 

 science to employ it as a vade mecum. It is characterised 

 by the manner in which broad and comprehensive prin- 

 ciples are grasped and illustrated ; entire groups are con- 

 trasted or compared, marched up and down as it were 

 like the skilful handling of battalions. Nevertheless, 

 whilst we cannot but admire the fearless manner of his 

 evolutions, we are afraid that Dr. Armstrong's love and 

 zeal for system and generalisation occasionally allure him 

 upon tender ground. The article is, presumably, not 

 specially written for chemists, although we have no hesi- 

 tation in affirming that every chemist who reads it will do 

 so with pleasure, and therefore hypotheses such as that 

 Epsom salts may be regarded as the normal magnesium 

 salt of dihydrated sulphuric acid, H^SO^, crystallised with 

 five molecules of water ; or that the true formula of potas- 

 sium perchlorate is KgClgOg ; or that th ~ molecule of 

 selenium dioxide is probably not represc ^ by the for- 

 mula SeOa ; or that the so-called hydrogei isulphide has 



presumably the composition H2S5 ; which are not the 

 common property of the science, however ingenious and 

 suggestive they may be, as these undoubtedly are, do not, 

 we submit, come within the scope of a treatise which 

 should primarily be a register of facts for the use of 

 general readers. We allow that Dr. Armstrong is 

 generally very cautious in his mode of stating these and 

 similar conjectures, and possibly a very careful reader, 

 whilst admitting their relevancy, would regard them in 

 their proper light of tentative hypotheses ; but all readers 

 are not careful ; the beaten path, we are told, is the safe 

 path ; and although scientific preachers, unlike other 

 preachers, may with impunity be as heterodox as they 

 please among themselves, it may be doubted how far it is 

 expedient to preach any other than perfectly safe doctrine 

 to the laity. This is really the only piece of adverse 

 criticism we have to offer. When facts are known they 

 are stated, and with remarkable perspicacity. As in- 

 stances of careful and judicious compilation we may refer 

 to the sections on ozone, hydrogen dioxide, and the 

 organo-silicon compounds. A commendable feature is 

 the recognition of the great importance of what we 

 have before termed the physical side of chemistry ; and 

 in this respect Di*. Armstrong's treatise is unique : we 

 have no hesitation in asserting that everything of value 

 which recent investigation in the domain of chemical 

 physics has brought to light is carefully interwoven in the 

 proper place. The results of the thermo-chemical work 

 of Thomsen and others ; of the work of Troost and 

 Hautefeuille and Brodie on dissociation phenomena ; of 

 the researches of Berthelot and others on the state of 

 salts m solution ; and of numerous other works scarcely 

 less important, are duly set forth, and in such relation as 

 to enforce their value and applicability. Indeed, in one or 

 two cases we have the results of work which has not yet 

 been fully published, as in the account of the action of 

 nitric acid upon the various metals. It appears that with 

 the exception of silver all the metals give with this acid a 

 mixture, in varying proportions, of free nitrogen and 

 nitrogen dioxide and monoxide. If, however, we com- 

 pare the behaviour of the acid in the case of the three 

 closely-related metals, magnesium, zinc, and cadmium, the 

 reducing action of the evolved hydrogen is found to be 

 greatest with the magnesium, and least with the cadmium, 

 which result Dr. Armstrong connects with the fact that in 

 the solution of these metals, the greatest amount of heat is 

 evolved by magnesium and the least by cadmium. But that 

 the comparative reducing power of the hydrogen evolved by 

 the action of the three metals stands in no direct relation 

 to the heat developed on solution, appears to be evident 

 from the circumstance that in the case of the deoxidation 

 of solutions of vanadium pentoxide by the action of these 

 metals, the very reverse obtains : magnesium added to the 

 solution of the pentoxide forms the trioxide, and the liquid 

 becomes green ; under no conditions, apparently, is this 

 metal able to bring about a lower degree of oxidation ; 

 on the other hand, zinc and cadmium carry the deoxida- 

 tion a stage further, and a lavender-coloured solution of 

 the dioxide is obtained. And it would further appear 

 from experiments which are in progress by the writer of 

 this notice, that the amount of hydrogen which is effec- 

 tive in the work of reduction, as measured by its power of 

 deoxidising ferric sulphate, amounts, in the case of zmc. 



