276 Proceedings of Royal Society of Edinburgh. [sess. 
It is evident from these figures that some butyrate clings ob- 
stinately to the propionate, and owing to its relative insolubility is 
precipitated first, the bulk of the propionate being found in the 
mother liquors. 
A qualitative reaction was next employed for the identification 
of the propionic acid. 
If this acid is boiled with excess of litharge and the solution 
allowed to remain in the cold for some time in contact with the 
litharge, a basic lead salt is produced, which is more soluble in cold 
than in hot water, and hence is precipitated on boiling the solution. 
Comparative experiments tried both with a known sample of 
propionic acid and with some of the fraction mentioned above, 
boiling between 125°-150°, give precisely similar results when sub- 
mitted to this test, a white powdery salt being precipitated from each. 
The three fractions obtained from the lower boiling portions of 
the acids obtained from the fermenting ulva were examined as 
follows. 
A roughly graduated pipette was made, and with it the same 
volume — about 0*2 c.c. — of each of the fractions was removed, 
weighed, diluted with water, titrated with 
N 
10 
baryta, the 
titrated 
fluid evaporated to dryness, and heated at 100° C. until of constant 
weight, then ignited with sulphuric acid, and the resulting barium 
sulphate weighed. 
The following table contains the results, calculated in such 
manner as to be comparable both with each other and with the 
theoretical quantities required for acetic, propionic, and butyric 
acid respectively. 
Fraction 
Acid taken 
c.c. Baryta 
required for 
1 part of acid 
Weight of 
dry Barium 
salt from 100 
parts of acid 
Percentage 
of Barium 
110°-125° 0. 
0*2430 grm. 
126*1 
177*3 
50*68 
125°-150° ,, 
0*2332 „ 
129*1 
189*7 
48*54 
150°-165° „ 
0*2192 ,, 
113*7 
182*2 
44*70 
c 2 h 4 o 2 
requires 
367*0 
212 
53*72 
c 3 h 6 o 2 
J 5 
135*0 
191 
48*41 
c 4 h 8 o 2 
113*6 
181 
44*05 
