246 Mr. W. R. Dunstan and Miss L. E. Boole. 



solution precipitated by water in three distinct fractions (A 1? A 2 , A 3 ), 

 the first (A^ and the last (A 3 ) of which were burned. 



A.i Weight of resin L648 



Weight of carbon dioxide . . 0*4028 

 Weight of water 0126 



= 66*6 per cent. ; H = 8*49 per cent. 



A 3 (1). Weight of resin 0*1992 



Weight of carbon dioxide . . 0*4736 

 Weight of water 0*4424 



C = 64*9 per cent. ; H = 7*94 per cent. 



A 3 (2). Weight of resin 0*1974 



Weight of carbon dioxide . . 0*474 

 Weight of water 0*1458 



== 65*4 per cent. ; H = 8*18 per cent. 



Mean for A 3 (1 and 2) C = 65*15 per cent. ; H = 8*02 per cent. 



These results show that the original resin (A) was almost pure, 

 since the composition of the first fraction (Aj) corresponds with that 

 pf the original (A), whilst between (A) and the last fraction (A 3 ) 

 is a mean difference of only 1-3 per cent, in the carbon, and 0*1 

 per cent, in the hydrogen. Combustion of different fractions 

 furnishes the most delicate, and in this case the only, available test 

 of homogeneity. The action of all three fractions on the skin was 

 exceedingly severe, and it was not possible to distinguish between 

 them. In order to gain conclusive evidence of the constancy of the 

 composition of croton-resin, a fresh quantity of croton oil was dealt 

 with in the manner previously described, and the resin purified by 

 fractional precipitation until it was obtained as a pale yellow hard 

 solid. The new specimen (B) on combustion furnished the following- 

 data : — 



I. C = 64*67 per cent. ; H = 7*94 per cent. 

 II. C = 64*6 per cent. ; H = 7*8 per cent. 

 Mean for B — 



C = 64*63 per cent ; H = 7*87 per cent. 



These results agree as well as could be expected with such a 

 material with the mean of those obtained with fraction (A : ,) in the 

 previous experiment ; and, taking the mean of these four combus- 

 tions of the two different specimens, we get 



C = 64*89 per cent. ; H = 7*94 per cent. 



