142 Dr. Thomson's Experiments to determine the f Aug. 



— — , or by 0*444, we obtain the weight of the peroxide of iron 

 present in the persuccinate. 



XII. Acetic Acid. 



This acid has given me more trouble than any other acid 

 whose atomic weight I have hitherto attempted to ascertain, 

 boracic acid alone excepted. I believe its weight to be 6*25, or 

 exactly the same with that of succinic acid. Probably the crys- 

 tals of acetic acid are composed of one atom acid + two atoms 

 water, and weigh 8'5 ; but I have not been able hitherto to verify 

 these conclusions by decisive experiments. 



The most careful analysis of acetate of lead which I was capa- 

 ble of making induced me to conclude that it is a compound of 



1 atom acetic acid = 6*25 



1 atom protoxide of lead = 14*0 



3 atoms water = 3*375 



23-625 



Hence I was led to expect that a solution of 23-625 grs. of 

 acetate of lead would be completely decomposed by being mixed 

 with 11 grs. of sulphate of potash, or 9 grs. of anhydrous sulphate 

 of soda ; but on trying the experiment, I found that the clear 

 liquid which covered the precipitated sulphate of lead was ren- 

 dered muddy by the addition of muriate of barytes. Hence it 

 obviously contained sulphuric acid in solution. I repeated this 

 experiment, gradually increasing the quantity of acetate of lead 

 till it amounted to 25 grs. yet the effect still continued ; but I 

 found that when nitrate of lead was dropped into the residual 

 liquor, the transparency was not affected. It was clear from 

 this, that acetate of lead does not possess the property of 

 throwing down the whole of the sulphuric acid from the solution 

 of a sulphate. I was of course obliged to abandon this method 

 of experimenting altogether. 



Fifty grs. of the crystals of acetate of lead were dissolved in 

 water, and precipitated by carbonate of potash. The precipitate, 

 after being well washed and dried on the sand-bath at a temper- 

 ature of about 500°, weighed 37-82 grs. It is evident from this, 

 that 23-625 grs. would have yielded 17-51 grs. of carbonate of 

 lead. Now 17-51 grs. of carbonate of lead contain 14*63 grs. of 

 protoxide of lead. This result did not accord with my supposi- 

 tion, that 23*625 grs. of acetate of lead contain exactly 14 grs. of 

 protoxide of lead. 



It is not possible, by the most careful experiments which I 

 have tried, to deprive acetate of lead of the whole of its water of 

 crystallization without, at the same time, driving off some of the 

 acid. 23*625 grs. when heated with every precaution, always 



