174 CAREY: GROSS STRUCTURE OF AN AGAR GEL 
hung up in the drier; others laid horizontally on the trays in the 
same at temperatures of about 43° C. and 70° C. Both of these 
showed the characteristic structure on swelling. Similar gels 
were dried at room temperature, 21-25° C., both stretched on 
frames and cut into strips. Some of the latter were either sus- 
pended or laid horizontally across supports. None of these 
showed any structure at all when soaked in water and sectioned, 
but were homogeneous throughout. A few of the gels dried at 
room temperature showed slight lamellations in places on the 
under side of the gel near the silk, but this was not so in all cases. 
It is apparent from the above, that the temperature and therefore 
perhaps the speed of drying may be an important factor in pro- 
ducing this lamellated structure. 
Gels of varying per cents of agar content were employed for 
this work, from 0.5—-10 per cent. They all showed structure when 
dried at 70° C. A 0.25 per cent gel was tried but was too weak 
to set at room temperature. The following concentrations of 
gels, expressed in per cent content of dry powdered agar, were 
used: 0.5, 0.75, 1, 1-5, 2.5, 3, 4, 5, 7-5, 8, and 10 per cent. The 
4 per cent gel was used to determine the point at which structure 
appeared as loss of water proceeded. 
It seems probable that this structure must form when a certain 
water concentration is reached in the drying of the gel. In order 
to ascertain at about what concentration the formation of struc- 
ture began and was complete, a 4 per cent agar gel was made 
and, when set, cut into pieces four by two and a half inches. 
Each piece was placed between a pair of tin frames which were 
held together by two elastic bands. Each frame had two holes in 
it one by one and a half inches. The whole apparatus with the 
agar was then put in the drier, for varying lengths of time, at a 
temperature of about 90° C. It was turned over at short inter- 
vals so that loss of water would be equalized on the two sides. 
The slices did not split during the process and were removed very 
easily from the frames. A portion of the pieces was cut off and 
put into distilled water; the other part weighed, put back into 
the drier and finally dried to constant weight in a calcium chloride 
desiccator. The part put into the water was sectioned after 
about twenty-four hours to see if there was any structure present. 
