Licence: Public Domain Mark
Credit: Manuals of food : food / Albert J. Bernays. Source: Wellcome Collection.
![151. When boiled for several hours even, bones give but a small proportion of gelatin; but, if placed with water in a Papin’s digester and heated to about 150° C., gelatin is very largely, if not completely, dis- solved. The more the bones are broken, the thicker is the jelly which is obtained, and also at an expense of less firing. 152. Gelatin is readily soluble in warm water; even one per cent, will cause water to gelatinize on cooling. Its solution is tasteless, and without odour. Alcohol precipitates it, and so also, but more com- pletely, does tannin; indeed leather is a compound of tannin with gelatin. From albumen and fibrin gelatin may be readily distinguished, in that it is not precipitated from its solution in acetic acid by yellow prussiate of potash. [See par. 143, enclosed in brackets.] 153. Gelatin contains more nitrogen and less car- bon than either albumen, fibrin, or casein ; like the latter it contains no phosphorus, but it contains more sulphur than casein. The composition of gelatin, it may be as well to contrast with casein, albumen, and fibrin. Gelatin. Casein. Albumen. Fibrin. Carboa .... .. 50-4 . .. 53-83 ... 53-50 ... 52-70 Hydrogen . . 6-5 . .. 7-15 ... 7-00 ... 6-90 Nitrogen.... . 16-9 . .. 15-65 ... 15-50 ... 15-40 Oxygen .... .. 25-6 .. 22’52 ... 22-00 ... 23-50 Sulphur .. 0-6 .. 0-85 ... 1-60 ... 1-20 Phosphorus none . none ... 0-40 ... 0-30 1000 100-00 100-00 10000 Clearly then, chemical analysis can tell us only the constituents of food; experience and judgment are required to make use of such analysis. For, if one thing be more certain than another, it is, that equal](https://iiif.wellcomecollection.org/image/b28063144_0073.jp2/full/800%2C/0/default.jpg)
