"20 Mr. PMUjps's Reply to Dr. Hope. [July, 



] atom of sulphuric acid 50*0 



1 atom of oxide of iron 44*5 



7 atoms of water 79-3 



Giving, as the number representing it, 173-8 



When this quantity of sulphate of iron is heated until it 

 becomes white, 69 parts of water are dissipated. It is, there- 

 fore, evident (making a small allowance for the error of experi- 

 i raent), that dried sulphate of iron consists of 



1 atom of sulphate of iron 94*5 



1 atom of water 11-32 



105-82 



As then 105-82 of the dry salt require 173*8 of the crystal- 

 lized, 12 ounces will require 19-7 ounces, the cost of which, as 

 supplied by the most respectable chemical manufacturers, will 

 rather exceed lOrf. 



Instead of purchasing acetate of lead of those who make it for 

 the purposes of the arts, you have directed it to be prepared by 

 dissolving carbonate of lead in vinegar which has been distilled 

 in glass vessels. In calculating the cost of the acetate of lead 

 thus procured, I shall suppose that none of the acetic acid which 

 vinegar contains is lost during distillation, and that it is all con- 

 verted without loss, and without expense of time, vessels, or fuel, 

 into acetate of lead. 



Acetate of lead is composed very nearly of 



1 atom of acetic acid 63-96 



1 atom of oxide of lead 139*50 



3 atoms of water 33 - 96 



Giving. 237-42 as the 



number representing this salt in the scale. 



That this is nearly the composition of acetate of lead, may be 

 seen by referring to the analysis of Berzelius ; and it is confirmed 

 by the proportion of sulphate of zinc which you have directed 

 for the decomposition of acetate of lead, viz. 60 parts of the sul- 

 phate to 80 parts of the acetate, instead of 79, as will be indicated 

 by the scale, provided I have mentioned the correct number for 

 acetate of lead. 



As then 237-42 parts of acetate of lead contain nearly 64 of acetic 

 acid, 10 ounces must contain very nearly 2-7 ounces of real acid. 

 One hundred parts of vinegar contain 5 of acetic acid ; to pro- 

 cure 2-7 ounces of acid will, therefore, require 54 ounces of 

 vinegar ; the cost of which, with the requisite quantity of car- 

 bonate of lead, will be about 15 d. 



I have repeatedly prepared your acidum aceticum forte, and 



