This section is from the book "Experimental Cookery From The Chemical And Physical Standpoint", by Belle Lowe. Also available from Amazon: Experimental cookery.
Gelatin is characterized by forming a solution in water at high temperatures and, with high enough concentration, a gel at low temperatures. The dry gelatin has a slightly yellow cast and contains from 10 to 18 per cent of moisture. It swells when put in cold water, the degree of swelling being modified by acids, alkalies, or salts. It dissolves at about 35°C, and it gels at low temperatures, the exact gelation temperature depending upon the concentration and time of standing.