216 Reviews, and Notices 7'especting New Books. 



of mercury with a metallic substance derived from ammonia or its 

 elements ; Dr. Wollaston's test for nitric acid; the undulatory theory 

 of light, &c. &c. 



Scarcely a page of the Chemical Catechism, it is observed by the 

 Editor, has been reprinted without some emendation : references, for 

 further information, to modern authorities, on all subjects of import- 

 ance, have also been given, where necessary. Many of the notes of 

 the former editions have been transferred to the text of the present, 

 and some of the former '* Additional Notes" have now been incor- 

 porated with the foot-notes or with the text. 



In order to enable our readers to form an opinion of the manner 

 in which Mr. Brayley has fulfilled his task, we proceed to extract 

 some of his additions, several of which, we may remark, appear to 

 have a value independent of that which they possess as parts of the 

 Chemical Catechism. Of the style of his additions to the text we 

 have an example in the Chapter on Caloric, in the subjoined reply 

 to the observation and request, 



" You stated that the two processes of the Conduction and the Radiation of 

 Caloj-ic frequently act in union in effecting an equal diffusion of heat, or in 

 producing the equilibj'ium of temperature : — Mention some familiar operation 

 in which this union exists. 



" Not only are the processes of conduction aud radiation often united 

 in the equal diffusion of heat, but that of reflection also, in many cases, is 

 exerted in conjunction with them, for the same purpose. Thus in the com- 

 mon operation of heating dinner-plates in a plate-warmer before a fire, 

 (which is only a case of the tendency to produce equihbrium of temperature, 

 the plates being heated in consequence of the tendency of the fire to diffuse 

 its caloric among the surrounding bodies,) all these processes are concerned. 

 The plates are heated in three ways; — by radiation from the fire and from 

 the plate-warmer itself, by reflection from the plate-warmer, and also by 

 conduction and communication from it. Of the radiant heat which is re- 

 ceived by the latter, a large portion is reflected upon the plates, especially 

 if the inside be very bright and clean; another portion is absorbed, and this 

 is gradually diffused by conduction throughout the utensil, and transferred 

 to the plates resting upon it, as well as in part also reflected [radiated] upon 

 them. In the former case, or in the passage of caloric from one body to another 

 in contact with it, the caloric is said to be communicated by the one to the 

 other, or to pass by communication. The same happens in many other fa- 

 miliar operations, and in those of the arts, as well as in the greater pro- 

 cesses of nature ; and that such must be the case in innumerable instances 

 will appear evident, when the existence in all things around us of reflecting 

 and radiating surfaces, of spaces occupied only by the air, through which 

 radiation takes place, and of solid bodies through which conduction takes 

 place, is considered." 



When treating of ammonia, Mr. Parkes had stated in the Cate- 

 chism itself, " If ammonia be decomposed in contact with mercury, 

 by means of galvanism, .... an amalgam of the mercury with a me- 

 tallic substance of a very uncommon nature may be procured from 

 this alkali." And in a note he had added the following particulars : 



" This experiment was first made in the year 1808 by the late Dr. See- 

 beck of Jena, and also about the same time by MM. Hisinger, Berzelius, 

 and Pontin, of Stockholm. Mercury, by combination with about one twelve- 

 thousandth part of its weight of new matter, is thus rendered a solid, and 

 at the same time so expanded in volume that its specific gravity is reduced 



