326 
rapidly in one direction than another causes 
an accumulation of a greater amount of gel- 
atine in the planes perpendicular to that direc- 
tion and hence more water can be absorbed 
and greater swelling take place. That this 
physical change was brought about by the 
evaporation of water and not by any natural 
change in the gelatine itself, was shown by 
comparative tests on the absorbing capacity of 
gelatine which was allowed to stand for 
twenty-four hours, with the absorbing capacity 
of gelatine which was exposed to the air for 
the same length of time. The first showed an 
equal swelling in all directions and the second 
the greatest swelling along the vertical axis 
(z. e., the direction of greatest evaporation). 
It seemed at first that gravity might be a 
strong force in determining the direction of 
greatest deposition and hence of greatest 
swelling, but the experiments reported upon in 
paragraph 4 above show that it is the amount 
of surface exposed to evaporation that deter- 
mines the direction of greatest shrinkage. 
Therefore, the vertical axis usually shows’ the 
SCIENCE 
[N. 8. Von. XLVIII. No. 1239 
TABLE I 
Inerease per em. of original thickness of pieces 
of gelatine which were made up as follows: lot 1, 
10 per cent. gelatine, 7. e., 1 gram of gelatine to 
9 grams of water; lot 2, 13 per cent. gelatine; lot 
3, 20 per cent. gelatine; lot 4, 33 per cent. gela- 
tine. All lots were allowed to attain the same 
water-content by exposure to air at 18-30° C. 
They were then placed simultaneously into dis- 
tilled water. The time column indicates the total 
times of immersion. Hach number is an average 
of measurements taken on six pieces. 
Time Lot 1 Lot 2 Lot 3 Lot 4 
16 hours....... 7.80 7.60 5.30 4.90 
40 hours....... 9.30 9.30 6.50 5.20 
64 hours....... 9.60 11.00 6.95 6.10 
88 hours.......] 11.00 — 7.30 6.80 
io shours een» 12.00 —_ 9.90 7.90 
136 hours.......] 13.20 — | 10.50 8.60 
160 hours....... 1 a= 11.60 10.25 
greatest shrinkage or swelling because of the 
custom of pouring gelatine into dishes open 
only at the top, or onto slabs where the largest 
evaporating surface is on top. A-.further in- 
: TABLE IL 
Change per em. in size of rectangular blocks of gelatine (length =2.00, height —0.35, breadth = 
0.35). 
(B) Same blocks dried with filter paper and allowed to lose water by evaporation. 
Ratios are given in brackets below numbers. 
again allowed to absorb water. 
(A) Blocks which have been tightly covered since time of setting, placed in distilled water. 
(C) Same blocks 
No. 1 No. 2 No. 32 
Time Notes 
Length Height | Breadth | Length Height | Breadth} Length Height | Breadth 
PANTS alameda savers 0.32 0.33 0.33 0.36 0.39 0.30 0.40 0.42 0.40 Increase. See 
(1.0) | (1.0) (1.0) (1.0) | (1.1) (0.8) (1.0) (1.0) (1.0) (A) above. 
Sphirsh ae: Waele onl 0.27 0.56 0.53 0.21 0.42 0.46 0.22 0.34 0.60 | Decrease. See 
(1.0) (2.1) | (2.0) | @.0) | (2.0) (2) Th GLOy |) Gia) 1) (eso) (B) above. 
15 hrs 0.25 0.47 | -0.53 0.26 0.55 0.52 0.24 0.38 0.58 | Increase. See 
(1.0) | @.9) | (2.1) (1.0) | (2.1) | (2.0) | @.0) | G.4) | (2.4) | (©) above. 
OUpDTSsey ee eae 0.31 0.61 0.66 0.32 0.55 0.66 0.27 0.43 0.49 | Increase. See 
(1.0) (2.0) (2.1) (1.0) (1.7) (2.0) (1.0) (1.6) (1.8) (C) above. 
68thrsk Mee lees 0.35 0.63 0.74 0.36 0.53 0.67 0.31 0.47 0.45 | Increase. See 
(1.0) (1.8) (2.1) (1.0) (1.5) (1.9) (1.0) (1.5) (1.5) (C) above. 
1Too soft for measurement. 
2In the entire experiment 27 blocks were used. 
Nos. 1 and 2 represent the behavior of 26 of them. 
No. 3 is given for two reasons: (1) to show that 
although the shrinking was somewhat differently 
distributed among the three dimensions, still the 
relation between shrinking and subsequent svwell- 
ing remains; (2) to give an idea of the variations 
which may be encountered when this method of 
measurement is used. Reference to the last will 
be made in a later paragraph. 
