No. 398.] SPECIFIC GRAVITY OF ANIMALS. 99 
I experimented with a Beaumé’s hydrometer to test how 
nearly the calculated values of my table matched the observed 
values of the hydrometer reading. One experiment began 
with water giving a hydrometer reading of 1.003. After dis- 
solving 5 grams of gum in 240cc. of this water, the hydrometer 
reading was 1.011. Deducting the discrepancy of the reading 
for the water taken, the true specific gravity of the solution was 
1.008. (The exact reading is difficult to be certain of, because 
of capillarity. I took the mean of a number of readings made 
by myself and by other persons reading independently.) By 
dividing the volume, 243.5 (counting one gram space as 0.7 cc., 
as in the tables), into the weight, 245, the specific gravity result- 
ing is 1.006+. So the hydrometer read nearly 0.02 higher 
than the calculated specific gravity. In another test, to 238 cc. 
distilled water at slightly more than 1.000 sp. gr., 5 grams of 
gum were added, whereupon the hydrometer stood at 1.010. 
The calculated gravity is 1.0062+, a little less than 0.004 
lower than the hydrometer reading. My results, then, are 
somewhat lower than the hydrometer would have made them. 
Taking into account the possible variation in the specific grav- 
ity of the gum, the two correspond quite closely. 
To determine whether different parts of a gum solution were 
of the same density, I tested a single mixture: 254 cc. of a 
solution in which the hydrometer stood at 1.037 were divided 
into upper and lower halves as gently as possible. To each 
half was then added its own volume of pure water. Testing 
each, it was found that the lower half had a specific gravity of 
1.020, while the upper read 1.018. As the solution had stood 
for some hours before being divided, I have assumed that the 
upper and lower halves of a solution were of the same density. 
I have written above each sp. gr. value in the table the frac- 
tion of the starting amount (in case of Table II 1 cc. of the 
gum-arabic mixture) which was added in the form of pure water. 
Taking, for example, the sixth place in Table II, the starting 
quantity of the mixture + 1.67 times its volume of water has a 
resulting specific gravity of 1.041. 
In performing an experiment I put 1 cc. of the gum mixture 
into a test.tube with a long pipette, taking care not to draw 
