336 



STARCH-PRODUCING PLANTS. 



11. Plantain . 



12. Arrowroot . 



13. Arrowroot . 



14. Tous led mois 



15. Tannia . 



16. Sweet cassava 



17. Msiise . 



18. Arrowroot . 



19. Hitter cassava 



20. Wheat starch 



16'23 

 1565 

 14 84 

 14'64 

 14-60 

 14*30 

 14-22 

 13 36 

 11'88 

 11-16 



C. L. 



C. L. 



Plantation Enraore 



C. L. 



C. L. 



C. L. 



0. L. 



C. L. 

 C., C. L. 

 Commercial, of English manufacture 



That the extremes in this table should occur in the case of the 

 starches of commerce, was, perhaps, to be expected ; nevertheless 

 the difference between the starch of the sweet potato and that of 

 the bitter cassava is nearly as great, and both these specimens were 

 prepared in the laboratory, by the same process, and subject to the 

 same temperature and exposure. 



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 takesa 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 fol- 

 lowing : 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 immedi- 

 ately poured into a conical test-glass,* which the jelly nearly iilled. 

 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, at- 

 tached 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 

 * The glasses used were all of the sort described in Griffin's catalogue under 

 the name of Clark's test-glasses. They were all, as nearly as possible, of the 

 same size and shape. 



p 



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