5. Guinea Yam (_D. aculeata_).--Grown in the same locality. Larger globules, elliptical; smaller ditto, spherical, often truncated; some shortly ovate, with the appearance of being flattened; general size and range, same as No. 4.

6. Barbados Yam, grown on banks of Demerara river. Globules, pear-shaped and mullar-shaped; range, 1-700 to 1-1,600; general size, 1-1,000.

7. Plantain (_Musa paradisiaca_).--Grown on the banks of the Demerara river. Globules long and narrow, generally long elliptical, often more acute at the ends than in any other species, some linear ended abruptly; length, often three times the width; range, from 1-400 to 1-4,000 of an inch; general size, 1-800.

8. Potato (_Solanum tuberosum_).--Irish tubers, from Belfast Sound.

Globules, 1-600 to 1-2,000; general size, 1-1,200.

9. Potato (Commercial).--Locality unknown. Range from 1-600; globules generally same as former, but a few stray ones as large as 1-40 of an inch.

10. Sweet Potato (_Convolvulus Batatas_).--Grown at the Lodge, Demerara. Form of globules, spherical aggregated; range, 1-1,000 to 1-4,000; general size, 1-2,400.

11. Arrowroot (_Maranta arundinacea_).--Specimens from Bermuda, where the highest priced and best quality is prepared. Ovate and elliptical; length in the larger globules, twice the width; range, from 1-800 to 1-2,400; general size, 1-1,400.

12. Ditto ditto, grown on plantation Turkeyen, Demerara, by J.W. King.

Size and description same as No. 11.

13. Ditto ditto, grown and prepared in Barbados. Characteristics the same, but globules more uniform in size.

14. Ditto ditto, grown on plantation Enmore; not quite so uniform in size.

15. Bitter Ca.s.sava (_Janipha Manihot_).--Grown on Haagsbosch plantation. A few globules occur as large as the 1-1,000 of an inch; these are ovate, the rest are spherical. The range is from 1-2,000 to 1-8,000; general size, 1-4,000.

16. Sweet Ca.s.sava (_Janipha Loeflingii_).--Grown on No. 1 Ca.n.a.l, Demerara River.

17. Tannia (_Caladium sagittifolium_).--Grown at the Lodge. Globules not so truly spherical as the foregoing, but range and size the same.

18. Wheat (_Tritic.u.m sativum_).--Locality unknown. Form of globules, spherical and slightly elliptical, some very small; range, 1-2,000 to 1-6,000, the former the general size.

19. Maize (_Zea Mays_).--Grown in the colony, but locality uncertain.

Globules, approaching to spherical, much aggregated; range, 1-2,000 to 1-4,000; general size, 1-3,000.

From an inspection of this list, it does not appear that the species would be easily distinguishable, and it is not easy briefly to describe the differences; in practice, however, and especially when the observer has a number of pure and authentic specimens before him, to have recourse to as standards of comparison, the discrimination is by no means difficult.

_Specific gravity of starch derived from various plants_.--Of many bodies the determination of the specific gravity is one of the best modes of distinguishing the purity. With the view of ascertaining whether the different varieties of starch have all the same density, as has been a.s.serted by some, trials were carefully made of as many specimens as I could procure. The results are embodied in the following table:--

TABLE No. I.--DENSITY OF STARCH DERIVED FROM VARIOUS PLANTS.

------------------+-------+-------+----------------------------------------- | |Tem. at| Names of |Density|time of| Remarks Plants | |Obs. F.| ------------------+-------+-------+------------------------------------ 1. Bitter ca.s.sava|1.4 3 | 87. |Grown in the colony and prepared in | | | the Colonial Laboratory.

2. Tannia |1.4773 | 87. |Ditto ditto 3. Arrowroot |1.4772 | 86.25 |Ditto ditto 4. Arrowroot |1.4748 | 86.25 |Ditto ditto 5. Common yam |1.4733 | 83.25 |Ditto ditto 6. Sweet potato |1.4718 | 85.75 |Ditto ditto 7. Arrowroot |1.4717 | 82.75 |St. Vincent's, commercial 8. Arrowroot |1.4701 | 84.75 |Grown in the colony and prepared in C.L.

9. Tous les mois |1.4698 | 85.25 |Ditto ditto 10. Sweet ca.s.sava |1.4692 | 86.5 |Ditto ditto 11. Wheat starch |1.4632 | 85. |Commercial, of English manufacture 12. Plantain |1.4615 | 85.75 |Grown in the colony and prepared in C.L.

13. Tous les mois |1.4611 | 84.25 |Grenada, commercial 14. Barbados yam |1.4607 | 83.5 |Grown in the colony and prepared in C.L.

15. Irish potato |1.4589 | 84.75 |Tubers from Belfast; prepared in C.L.

16. Guinea yam |1.4581 | 84.2 |Grown in the colony and prepared in C.L.

17. Potato |1.4561 | 84. |Commercial 18. Buck yam |1.4489 | 81.25 |Grown in the colony and prepared in C.L.

19. Arrowroot |1.4443 | 85.5 |Barbados, commercial 20. Arrowroot |1.4158 | 86.25 |Bermuda, ditto 21. Maize |1.4109 | 85.5 |Grown in the colony and prepared in C.L.

From this it will be seen that the order of density does not correspond with the order in any of the other tables. Probably those specimens prepared from dry seeds, such as wheat and maize starch, which, as commercial articles at least, are less pure than those prepared from recently dug roots, have also the lowest density.

_Hygroscopic properties of starch produced from different plants_.--Such of the specimens as are marked in the following table, as prepared in the colonial laboratory, were dried in the sun in shallow trays, to which they had previously been transferred in the wet state. When sun dried, the ma.s.ses were broken down, and the starches freely exposed to the air in the shade for ten days. Any adherent ma.s.ses were then rubbed to powder by light pressure in a glazed mortar, and the whole sifted. Portions of each of these starches, and of others for the sake of comparison, were then dried, at 212 degrees Fahrenheit, in a current of dry air, and the loss determined:--

TABLE No. II.--SHOWING THE HYGROSCOPIC WATER CONTAINED BY STARCH PRODUCED FROM DIFFERENT PLANTS.

Per centage of water. Remarks.

1. Potato 20.27 Commercial, locality unknown 2. Sweet potato 19.57 C., C.L.**

3. Buck yam 19.43 C., C.L.

4. Barbados yam 19.40 C., C.L.

5. Arrowroot 18.81 Bermuda, commercial 6. Irish potato 17.28 Tubers from Belfast, C.L.

7. Guinea yam 17.14 C., C.L.

8. Tous les mois 16.74 Grenada, commercial 9. Arrowroot 16.43 Barbados, ditto 10. Common yam 16.36 C., C.L.

11. Plantain 16.23 C., C.L.

12. Arrowroot 15.65 C., C.L.

13. Arrowroot 14.84 C., Plantation Enmore 14. Tous les mois 14.64 C., C.L.

15. Tannia 14.60 C., C.L.

16. Sweet ca.s.sava 14.30 C., C.L.

17. Maize 14.22 C., C.L.

18. Arrowroot 13.36 C., C.L.

19. Bitter ca.s.sava 11.88 C., C.L.

20. Wheat starch 11.16 Commercial, of English manufacture

[** The initial C. throughout these tables indicates that the plant was grown in the colony; C.L., that the starch was prepared in the colonial laboratory.]

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 ca.s.sava 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 takes a much larger quant.i.ty 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 ca.s.sava 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-gla.s.s,[45] which the jelly nearly filled. The time at which each gla.s.s was filled was noted, and exactly two hours were allowed for the contents to cool in a current of air. The gla.s.s is then set on a plate of gla.s.s, 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 bra.s.s 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 gla.s.s 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 gla.s.s on which the test-gla.s.s 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. 895 5. Irish potato, from Belfast, C.L. 756 6. Tannia, C., C.L. 630 7. Bermuda arrowroot, finest Commercial 627 8. Common yam, C., C.L. 657 9. Guinea yam, C., C.L. 571 10. Plantain, C., C.L. 467 11. Potato starch, Commercial 467 12. Arrowroot, C., C.L. 393 13. Sweet potato, C., C.L. 368 14. Arrowroot, C., C.L. 340 15. Arrowroot, C. 301 16. Arrowroot, St. Vincent's, Commercial 289 17. Barbados arrowroot, Commercial 273 18. Wheat starch, Commercial 183 19. Buck yam, C., C.L. 151 20. Bitter ca.s.sava, C., C.L. 150 21. Sweet ca.s.sava, C., C.L. 78

[* In this instance the weight stated detached the jelly from the side of the gla.s.s, but the skin of the jelly was not torn as in the other cases.]

From this list it is obvious that, in respect of tenacity, there is a very great difference between the jellies prepared from the different starches--greater, indeed, than exists in regard to any other character. At first I thought it probable that the tenacity of the jelly would bear some relation to the size of the globules, and it is true that we find the Grenada Tous les mois, the largest globule, next the top, and the ca.s.sava among the smallest, at the bottom of the scale. But, on the other hand, we have the Buck yam starch, a large sized globule, very high; together with many other exceptions.

As an article of diet, the most tenacious varieties of starch are preferred, on account of the economy of employing an article of which a less quant.i.ty will suffice; and the same is true when applied to starching linen, provided the jelly be not deficient in clearness.

_Clearness of jellies_.--When starch jelly is used for the purpose of starching, or glazing linen, or cotton goods, those varieties that are most transparent are understood to be preferred, provided, at the same time, they possess the requisite tenacity. This and other matters will be best determined by practical men in England; but having had occasion many times to prepare specimens for trying the tenacity, the opportunity was always taken of arranging the specimen of jellies in the order of their clearness, or, to speak more accurately, of their translucency. In this respect also they exhibit considerable differences, varying, when prepared according to the formula described under the head of tenacity, from very translucent approaching to opaque. The order is shown in the annexed list, which begins with the clearest.

TABLE NO. IV.--SHOWING THE ORDER OF CLEARNESS OR TRANSLUCENCY OF UNIFORMLY PREPARED STARCH JELLIES.