272 Proceedings of Royal Society of Edinburgh. [sess. 
The fermentation of grape sugar by the Bacillus butyricus is 
usually represented by the equation 
C 6 H 12 0 6 = 2C0 2 + 2H 2 + C 4 H 8 0 2 ; 
and, as we have already mentioned, before we had made any gas 
analyses, the production of butyric acid had been indicated. 
A qualitative examination of the contents of the flask after 
fermentation gave further evidence of the production of the acid, 
for on distilling them with sulphuric acid an acid liquid passed over, 
and this, when neutralised with soda and evaporated to dryness, 
gave a solid residue, which, when warmed with strong sulphuric 
acid, emitted a distinct odour of butyric acid. Also when it was 
warmed with strong sulphuric acid and alcohol, the characteristic 
odour of butyric ether became apparent. 
We should probably not have pursued the question further had 
it not been for the results of a quantitative analysis of what we 
supposed to be calcium butyrate obtained as follows : — 
Some of the ulva was well washed and packed into a flask, which 
was then filled with sea water and the mixture fermented in an 
incubator at 37° C. until gas evolution ceased. The liquid was then 
strained off from the seaweed through a cloth filter, distilled with 
sulphuric acid, the distillate boiled with excess of calcium carbon- 
ate, filtered, and evaporated to dryness. Weighed portions of the 
carefully dried residue were then ignited with strong sulphuric 
acid, with the following results : — 
0*2546 grm. gave 0T883 grm. CaS0 4 = 0*0554grm.Ca = 21*75% Ca. 
0*3695 „ 0-2681 „ =0-0788 „ =21*34 „ 
Anhydrous calcium acetate requires 25*32% Ca. 
„ „ propionate requires 21*50 „ 
„ „ butyrate „ 18*70 „ 
These results indicated that propionic and not butyric acid had been 
produced, and the matter seemed worth further investigation, as there 
appears to be some doubt as to a propionic fermentation from crude 
vegetable substances, and it is certainly not mentioned in modern 
chemical or bacteriological text-books. On the other hand, in the 
older chemical works such a fermentation is mentioned. Thus in 
