91 
of crystallization, and the anhydrous zinc sulphate cal- 
culated into the crystalline or hydrated zinc sulphate; 
these prescriptions, then, contained no ingredient which 
could interfere with the direct determination of the salt 
introduced. I give the dispensers, in this paper, the 
advantage of not estimating the actual proportion of 
the pure salt, hut the total, of what had been added 
by them. The first prescription should have been 
made up to a total fluid measure of 6 ounces (2625 
grains) which quantity should have contained 120 grains 
of potassium iodide. The second prescription should 
have been made by adding 40 grains of crystallized zinc 
sulphate to 2 ounces of water, which would make a total 
fluid measure of 893 grains, but as few gave either the 
exact measure of liquid, or weight of solid, I found it 
necessary to make three columns of figures, in the following 
tables, for each prescription $ the first to show the amount 
of liquid measured out; the second to show the total 
amount of solid weighed out ; and the third, as a comparison 
of the actual strength of the different fluids, which is made 
by calculating the amount of potassium iodide which would 
be contained in exactly 6 ounces (2625 grains measure) of 
the mixture, and the amount of zinc sulphate which would 
be contained in exactly 893 grains measure of the lotion, 
supplied by each druggist. 
It will, of course, be clearly seen, that if the potassium 
iodide or zinc sulphate were damp, or in bad condition, 
although the weighings may have been made with absolute 
accuracy, the actual amount of the salts found on analysis 
would be less than that weighed ; but this is equally a fault, 
because dispensers ought to have all their drugs in good 
condition. The following table will show the results of the 
analysis of eighty-one samples of the potassium iodide 
mixture, and the same number of the zinc sulphate lotion, 
one sample of the mixture, and one of the lotion, havino- 
