Characters of the jellies formed by various starches.—­Tenacity.—­I have met with no very precise results on this subject, except the well-known fact that it takes a much larger quantity of some starches, the arrowroot for instance, to form a jelly of equal tenacity with that formed by others, such as the Tous les mois; and hence in the West Indies the latter is universally preferred to the cassava starches.

After trying various plans, the method which I found best fitted for comparing the tenacity of different starch jellies, was the following:—­Of each of the kinds of starch, 24 grains were weighed out and mixed with 400 grains of distilled water, in a porcelain capsule of suitable size.  The mixture was then heated and boiled briskly for three minutes, with constant stirring, and was immediately poured into a conical test-glass,[45] which the jelly nearly filled.  The time at which each glass was filled was noted, and exactly two hours were allowed for the contents to cool in a current of air.  The glass is then set on a plate of glass, supported on a ring of a retort stand, and the weight ascertained, which was necessary to force a metallic disc, of ascertained size, through the jelly.  The most convenient way of doing this was by using a piece of apparatus of the form rudely represented on the margin.  The rectangular frame is of thin brass wire, and the slightly cup-shaped disc, d d, is soldered to a wire, attached to the upper short side of the rectangle.  From the opposite or lower side of the rectangle a small glass cup, c., is suspended, into which weights are put as soon as the disc has been made to rest on the surface of the jelly, pp is the plate of glass on which the test-glass is set.  Whenever the disc tears the skin of the jelly and begins to sink in it, no further addition, of weights is made, and the weight of the disc, framework, and cup being known, we have an estimate of the tenacity of the jelly.  This process is but approximative, and some practice is necessary before the operator succeeds in getting uniform results from the same series of specimens.

+--------------------+
|          |         |
|          |         |
|          |         |
|    d  \_____/  d   |
|                    |
|                    |
|                    |
|  p--------------p  |
|                    |
|                    |
+--------------------+
|
|
|
|
---------
c.

The following statement shows the results on such specimens as I could procure.  The disc was exactly 7/10ths of an inch in diameter.

TABLE NO.  III.—­TENACITY OF STARCH IN JELLIES.

No.  Names of specimens.  Weight in grains required
to break the jelly.
1.  Tous les mois, C., C.L. 2,446*
2.  Tous les mois, Grenada, Commercial 1,742
3.  Maize, C., C.L. 955
4.  Barbados yam, C., C.L.