Notices respecting Neiv Boohs. 61 



From these instances it will be seen that Dr. Apjohn's lists of 

 "known compounds" include many substances with which other 

 chemists are by no means well acquainted : hence it is natural that 

 he should require to make room for them by ignoring substances 

 which often receive a considerable share of attention. Thus 

 (p. 502) the usual list of hydrocarbons is very much curtailed : we 

 are told that " The number of compounds of carbon and hydrogen 

 is very great. Those at present known are reducible to three 

 groups : — Those whose general formula is C n Hn, those represented 

 by C n H n+1 , and those by C n H n+2 » n being always an even number." 

 Again (pp. 463, 464), "The only known compounds of boron with 

 the metalloids are the teroxide, tersulphide, terchloride, and ter- 

 fluoride." Surely Dr. Apjohn has heard of nitride of boron. No 

 similarly distinct assertion is made of the non-existence of hydride 

 of silicon and of the whole series of compounds corresponding with 

 an oxide containing half as much oxygen as silica, discovered a few 

 years ago by Wohler ; but, from the absence of the slightest allusion 

 to any of these interesting substances, we must suppose that their 

 existence is not yet recognized by our author. 



If, from the enumeration of the compounds of the various elements, 

 we turn to the detailed description of their properties and reactions, 

 we find no greater accuracy. We will quote but one passage in 

 illustration of this remark. It occurs on pages 561 and 562, and 

 refers to the volumetric process for estimating cyanogen, in presence 

 of excess of potash, by means of a standard solution of nitrate of 

 silver. "The free potash will develop oxide of silver; but this is 

 immediately taken up by the cyanide of potassium, with a view [sic] 

 to the formation of the double cyanide ; so that, as long as there is 

 uncombined cyanide of potassium, there will be no permanent pre- 

 cipitate. But when the cyanide of potassium is altogether con- 

 verted into the double cyanide of potassium and silver, if any addi- 

 tional quantity of the nitrate be added, the oxide of silver separated 

 from it by the potash will appear as a permanent precipitate." It is 

 difficult to suppose that the writer of this passage has ever performed 

 the operation he professes to describe, otherwise he could hardly 

 have failed to notice that in reality it is the white cyanide of 

 silver, and not the brown-grey oxide which " appears as a perma- 

 nent precipitate." 



But the most remarkable portions of Dr. Apjohn's work are those 

 in which he has occasion to refer to the past history of the science, 

 or to record his opinion of the works of his contemporaries. At 

 page 124, for instance, the relation of Lavoisier to the antiphlogistic 

 system of chemistry is placed in a new light. " Stahl conceived that 

 combustible bodies, such as carbon, sulphur, phosphorus, and iron, 

 included a fiery principle, which he called phlogiston ; and that, 

 when they underwent combustion, the fiery principle is evolved. 

 This phlogistic theory is at the present day only interesting in con- 

 nexion with the history of chemistry. It held, however, its ground 

 for a long time, and was only abandoned when it was shown by 

 Ray and Mayow that bodies in burning, instead of becoming lighter, 

 augment in weight. 



