TESTING GELATINE.
The selection of a suitable gelatine is a most important matter. A good plan is to obtain a variety of sample's, and test their melting point. The following is a simple and ingenious method of testing gelatine. A solution is made of each of the gelatines under examination, and a small layer taken by means of a paper tube worked on the principle of a pipette. That is to say, a tube having about 1 in. bore is lowered into the solution to the depth of the first method being the better of the two. Small thermometers are now placed against, the inside of the vessel, as near as possible to each disc of gelatine, and the water very slowly heated. The tem perature at which the gelatine melts, which is indicated by its detachment from the side of the vessel, must be carefully noted. Against each sample of gelatine the name should he written, to prevent possibility of confusion. This experiment will not only enable a rough classification into hard and soft gelatines to be made, but will determine the exact melting tempera ture of the different varieties used. A
mark should be made on the vessel to about in., the top of the tube being closed with the tip of the finger to make it air-tight (see Fig. 266). It is then rapidly withdrawn and laid over one side of a flat-sided vessel, and the finger removed (see Fig. 267). This de posits the gelatine in a form somewhat resembling a gelatine lozenge on the side of the vessel, to which it adheres. firmly. Each sample of gelatine is treated in the same way, and the vessel is then filled with water, and either placed over a stove or supplied with hot water from the tap show clearly when the gelatine disc corn- I mences to move, and the hot air from the burner should be shielded from the out side.