Thomson's Sj/stem of Chemistri/. 167 



of pure silver*." But Klaproth gives here 88.75 of mu- 

 riate of silver, which are equivalent to 66.87 of metal. The 

 Doctor's erroneous number 87.75, is not equivalent to 65.81, 

 as he asserts, but to 66.11, computed from his own atomic 

 weights. 



Under analysis of red copper ore, he says, " 88 parts of the 

 precipitated copper being equivalent to 100 of the orange oxide 

 of which the ore is composed." Now 88 are equivalent to 99, 

 not 100. " The analysis of the oxides and carbonates of 

 copper," says he, " scarcely requires any remarks. The water 

 and carbonic acid, must be estimated by distillation in close 

 vessels, and collecting the products. The ore may then be 

 dissolved in nitric acid, and its copper ascertained as abovef." 

 This is all he says; and what can a student make of it? The 

 quantity of carbonic acid is to be estimated by the loss of 

 weight, which 100 grains of the ore sustain during their solu- 

 tion in dilute nitric acid; and the proportion of water is found 

 by subtracting that quantity from the total loss of weight, 

 which another 100 grains suffer by ignition. But if arsenic, 

 or other volatile matter, be suspected, the water may be esti- 

 mated at first, by a regulated desiccation. Under the Analysis 

 of Arseniate of Copper and Iron, he says, " Nitrate of lead 

 was mixed with the solution; 100 parts of the precipitate 

 indicated 33 of arsenic acid." Now by Berzelius's estimate, 

 which he adopts in his first volume, 100 are equivalent to 

 33.52. 



" Tin-stone," says he, " was thus analyzed by the same cele- 

 brated chemist, (Klaproth); 100 parts of the ore were heated 

 to redness with 600 parts of pot-ash in a silver crucible l" 

 Klaproth says, " One hundred grains of tin-stone fromAlternon 

 in Cornwall, previously ground to a subtile powder, were mixed 

 in a silver vessel with a lixivium, containing 600 grains of 

 caustic potash. This mixture was evaporated to dryness in a 

 sand-heat, and then moderately ignited for half an hour §." 

 By following Dr. Thomson's misdirection, a satisfactory analysis 

 cannot be made. 



Of three different ores of antimony, he gives three plans 

 of analysis, two of which are copied from Klaproth, and the 

 third must he his own. The whole are, however, erroneous as 

 given by Dr. Thomson. " Native antimony," says he, " was 

 thus analyzed by Klaproth ; 100 grains were digested in nitric 

 acid, till the whole was converted into a white powder ; when the 

 acid emitted no longer any nitrous gas, the mixture was diluted 

 with water, and thrown upon a filter. The solution was then 

 treated with nitrate of silver. The precipitate yielded by re- 



* Si/slem, flili Edilion, III. (J05. t ll)iil., III. (j'08. 



X Si/flrm, III. IM'J. j Analytical Essays, I. li'LV, English iraiislation. 



