SPECIFIC GRAVITY AND FERMENTATION. 
39 
ing liquor. However, these readings can not be implicitly relied upon 
because of the variable quantity of nonfermentable solids. No one 
has yet been able to devise a method by which gravity determinations 
can be made to indicate composition with chemical accuracy, but the 
table published on page 89 of Bulletin 71, Bureau of Chemistry, seems 
to €ome within such reasonable bounds of accuracy that it may be 
used as a guide in the fermentation room. 
With a view to illustrating the use of this cellar table all the 
hydrometer readings taken during fermentation of the ciders made at 
this station, the chemical analyses made at the several stages of fermen- 
tation, and the approximate percentages of sugar and alcohol deter- 
mined theoretically, have been arranged in parallel columns in Table 
VII. In those instances where only a hydrometer reading is given 
there is of course no comparison, but Adhere alcohol and sugar deter- 
minations were made the comparison is direct and interesting. In a 
■considerable number of instances the calculated or approximate per- 
centages are close indeed to those actually determined by analysis, but 
in several instances they are wide apart. The peculiarities of yeast 
races has to do with this matter, as we have definitely proved that cer- 
tain yeasts are able to produce a higher percentage of alcohol in 
identical musts than others. Also, when the theoretical table was com- 
piled it was assumed that the nonsugar solids always exceeded 2 per 
cent in normal must and ciders, but this does not appear to be always 
true, as shown by the analyses of the special ciders made with pure 
yeasts at this station. 
Table VII. — A comparison of gravity determinations and analyses made at various stages 
of fermentation, with the percentages of sugar and alcohol calculated from gravity read- 
ings alone. « 
WORK OF 1901- 
Date. 
Sample. 
Specific 
gravity. 
Grams per 100 cc as determined 
by analysis. 
Approximate 
percentages as 
calculated. 
Total 
solids. 
Sugar- 
free 
solids. 
Total 
sugar. 
Alco- 
hol. 
Total 
sugar. 
Alco- 
hol. 
September 24 
Original must . . 
Test No. 2 
do 
1.050 
1.026 
1.006 
1.007 
1.004 
1.020 
1.003 
1.003 
1.003 
10.15 
5.35 
1.35 
1.55 
.95 
4.15 
.75 
.75 
.75 
0.00 
6.80 
1.98 
4.82 
1.-16 
1.02 
.98 
4.16 
.27 
.30 
.20 
2.76 
4.68 
4.44 
4.43 
3.21 
5.36 
5.09 
5.20 
2.40 
4.40 
do... 
2.87 
2.60 
5.72 
1.85 
1.62 
1.56 
4.30 
May 16 
...do... 
4.60 
OctobeT 4 
November 23 
Test No. 3 
do 
3.00 
4.70 
do 
2. 33 
2.24 
2.03 
2.04 
4.70 
May 22 
do 
4.70 
a For table of hydrometer readings, see page 89, Bui. No. 71, Bur. of Chem., U. S. Dept. of Agr. 
