i^8 Mr. Chenevix’s Analysis of 
To the use of alcohol, in order to get rid of the excess of 
acid, as mentioned above, there is not the same objection that 
there might be to evaporation, or to an alkali : it can combine 
with that acid only which is free ; and an excess of it can, in 
no way, affect the metallic salts. 
I have given the preference to lead, above every other method 
of combining arsenic, to determine its quantity in any other 
body, having found arseniate of lime, which has been hitherto 
recommended, as well as all other earthy arseniates, to be 
nearly as soluble in water as sulphate of lime. Lead presented 
also much facility as to the proportions of its arseniates ; and a 
few experiments, instituted to arrive at them, afforded sufficient 
accuracy. But, first, it was necessary to ascertain how much 
acid a given quantity of metallic arsenic could afford; and, 
finding that it was in vain to aspire at a greater degree of 
precision, than that which Mr. Proust had obtained, I have 
adopted his results. By them it appears, that 133 of white 
oxide, and 153 of acid, contain each 100 of real arsenic, the 
rest being oxygen. But, 100 of metallic arsenic, acidified by 
nitric acid, neutralized by an alkali, and precipitated by nitrate 
of lead, gave 463 of arseniate of lead ; that is, 100 of arseniate 
of lead, contain 33 and a fraction of arsenic acid ; and, on the 
other hand, my own experiments informed me, that lead, dis- 
solved in nitric acid, and precipitated by arseniate of ammonia, 
seeking silica, or alumina, by ammonia, no trace of them can be found, nor indeed of 
any thing else. I do not say, however, that the potash is perfectly free from every other 
substance ; I believe it contains a little carbone, produced by the decomposition of the 
alcohol, and is, therefore, a subcarburet of potash ; but carbone can be of no conse- 
quence, in the generality of experiments, in humid docimasia. The same method, 
employed with carbonate of soda, is the only one to procure soda in a state of equal 
purity. 
