1824.] upon the preceding Answer. 129 



represents it as " constituted of three atoms of hydrogen = 3 + 1 

 atom of nitrogen = 14 ;" and Mr. Brande, of " 13 of nitrogen and 

 3 of hydrogen." (Manual, vol. i. p. 364.) That Goulard's extract of 

 lead is a sub-binacetate and not a subtritacetate is an assertion 

 which I again repeat. You will observe that three authors out 

 of four whom you quote in support of your opinion, infer the 

 composition of this acetate of lead, not from analysis, but from 

 an experiment of Berzelius ; the fourth authority, Mr. A. T. 

 Thomson, is so far from asserting this compound to be a subtrit- 

 acetate, that he quotes the very analysis upon which I founded 

 my conclusion of its nature. Mr. Thomson says (London Dis- 

 pensatory, p. 693), "According to the experiments of Dr. Bos- 

 tock, the constituents of ] 00 parts of the saturated solution are 

 23*1 of oxide, 5 acetic acid, and 71*9 of water, which," he adds, 

 " agree with the statement of Thenard, who found that the salt, 

 when crystallized, consists of 17 parts of acid, 78 of oxide of 

 lead, and 5 of water, in 100 parts." Now it will appear, that 

 the quantities of acid and oxide by Dr. B.'s analysis, are to each 

 other in the proportion of 50 acid and 231 oxide; and in The- 

 nard's analysis as 50 to 230, very nearly. According to Dr. 

 Thomson, Dr. Henry, and Mr. Brande, acetate of lead is com- 

 posed of 50 acid +112 oxide ; and you will, perhaps, admit that, 

 supposing Goulard's extract to be a sub-binacetate, it must consist 

 of 50 acid + 224 oxide ; but if a subtritacetate of 50 acid + 336 

 oxide; the question, therefore, depends upon whether 231 or 

 336 are nearer to 224, and I think I may safely leave it to you to 

 decide. 



I must again insist that at p. 81 of your Elements, no rules are 

 given for describing those salts that contain an excess of base. 

 The 14 lines to which you allude have not slipped out of my 

 copy ; but if these 14 lines ever contained a syllable respecting 

 sub-bisalts or sub-trisalts, such syllable has indeed disappeared. 

 In p. 94, to which you refer me for a continuation of the subject, 

 all that is contained respecting it is, that to express the number 

 of charges, the terms employed are, " subsesquiphosphate, sub- 

 bisulphate, for salts with excess of base." Not a word occurs 

 respecting subtrisalts, those which occasioned the remark that I 

 made. I admit that in p. 151 of the Elements of Pharmacy, 

 there is a paragraph which treats of the metallization of white 

 arsenic by the addition of " astibcarbonateofpotasse and charcoal 

 dust ;" but I deny that it has any connexion whatever with the 

 subject of detecting arsenic. It is stated without reference to 

 it, and just as you would mention the reduction of any other 

 oxide : indeed totally imperfect as the method which you had 

 previously stated is, it is given without any reservation, and as 

 possessing such a degree of certainty as would render all addi- 

 tional proceedings useless. 



When I asserted that you had not noticed the decomposition 

 of water, and the formation of phosphorous acid, which occur 



Neiv Series, vol. vii. k 



