July 13, 1883.] 



♦ KNOWLEDGE ♦ 



19 



ture ; writing with that instrument before me, let me 

 describe the observation I have just made. Having 

 obtained a little potato starch, and, in addition, some 

 arrowroot (also a starch), I placed a drop of water on 

 a clean slide, then the smallest pinch of starch, and, 

 finally, very gently iiressed down a cover glass. I then 

 looked at each sample with an eighth objective. Taking 

 the potato starch, it is readily seen to be composed of little 

 granules ; some of these are spherical, others, wliich are 

 older, are shrivelled, and have polygonal outlines ; some of 

 the more favourably-situated corpuscles show a series of 

 ring-like markings. This latter peculiarity points to the.se 

 particles having a concentric structure, somewhat like that 

 of an onion. Viewed by polarised light, with crossed nicols, 

 a black cross is seen in each granule. Looking at the 

 arrowroot, the first point noticed is that the granules are 

 larger, and of a different shaped outline. Their form re- 

 minds one of the shape of a mussel-shell, and the ring-like 

 markings start, like those of the shell, from a point near one 

 end ; using polarised light, the black cross is again seen 

 distinctly, but its arms are no longer at right angles ; the 

 centre of the cross also coincides with the point around 

 which the markings are concentric. 



These little starch corpuscles of which we have been 

 writing consist of an outer envelope of starch cellulose, a 

 substance closely allied to starch, and of granulose, or starch 

 proper, which constitutes the interior of the granule. Starch, 

 as far as we know, is not dissolved without change by any 

 known liquid. This is, in fact, exactly what we might 

 expect, because starch possesses an organised structure ; 

 when once that is destroyed by solution, it can never be 

 restored liy simply driving off the liquid ; for though by 

 evaporation we may thus obtain, of certain substances, 

 crystals of perfectly regular shape, it is impossible, without 

 the aid of life, to build up organised structures. Cold 

 water is aVisolutely without action on starch ; but take 

 a small quantity aud, having shaken it up with water, 

 gradually heat, the starch swells up and forms a 

 thick paste. By the action of heat, the starch 

 granules are ruptured and the interior granulose dis- 

 solves ; the addition of a large quantity of water 

 renders the starch almost entirely soluble ; the little 

 envelopes, however, remain, and may be filtered off' from 

 the solution. It is a matter of uncertainty as to whether 

 this soluble starch is chemically or only mechanically dis- 

 tinct from the insoluble form. Before dealing further with 

 the chemical constitution of starch, it will be well to 

 inquire a little into how starch is oVitained from the dif- 

 ferent substances containing it. If a small quantity of 

 wheat>fiour lie taken and wrapped in a piece of muslin, and 

 then kneaded between the fingers in a small basin of water, 

 the water becomes milky, and there remains behind, within 

 the muslin, a tough glutinous substance, termed gluten. 

 Of this we shall have to say more a little later. Let now 

 the water stand ; it gradually becomes clear, and deposits , 

 a white powder at the bottom of the basin. If now the 

 water is poured ofl^, and the powder allowed to stay, a 

 fairly pure sample of starch is thus yiiOded. lu 

 manufacturing starch on the large scale, wlieat is 

 first coarsely ground, and then wetted with w\ater ; on 

 being allowed to stand for some days, fermentation sets 

 in. The wheat is then transferred to large vats, and addi- 

 tional water added ; fermentation goes on apace, and the 

 gluten putrefies, evolving a most offensive odour. Certain 

 acids (acetic and lactic) are formed as a result of 

 fermentation, and these dissolve any remaining gluten. 

 The remaining starch is next thoroughly washed and sub- 

 se.quently dried. During the latter operation the masses 

 pf starcli shrink and split up into the columnar structure 



so well known in laundry starch. A considerable quantity 

 of starch is also manufactured from the potato. The 

 principle is much the same : the tubers are first washed, 

 then i-asped into a pulp, and washed on a sieve ; the water, 

 which runs through milky, from the presence of starch 

 granules, is allowed to stand until it deposits its starch ; 

 the sediment is then carefully washed and dried. As 

 the potato contains no gluten, the process of putre- 

 faction necessary with wheat is not required. It 

 was before mentioned that " corn-flour " is the starch 

 of maize ; in its preparation the disagreeable method of 

 removing gluten liy putrefaction is avoided by using a very 

 dilute solution of soda as a solvent for that compound. 

 The gluten is thus first dissolved out, and the remaining 

 starch is washed and dried. In this manner is yielded a 

 very pure and elegant form of starch. While, as a pre- 

 paration of starch for food-purposes, corn-flour leaves 

 nothing to be desired, it should never be forgotten that it 

 is, after all, starch, and starch only. That cheapest form 

 of starch, viz., that of the potato, has recently been brought 

 into the food market under the name of " potato fecule ; " 

 fecule, be it remembered, is simply the French name for 

 starch. A glance at the table given at the head of this 

 paper shows rice to be almost entirely composed of starch. 

 For the great majority of purposes where starch is re- 

 quired as an article of food, there is no better substance to 

 use than rice, either in the form of the whole grain or 

 ground into meal by passing through a small hand-mill. 

 The difi'erence in cost of rice compared with that of these 

 other staich products is well known to every prudent 

 housewife. 



GEOLOGY AND AGRICULTURE. 



By J. ViNXEN-T Elsdex, B.Sc. (Lond.), F.C.S. 



11. 



ri^lHE quantity of water carried down Ijy rivers depends 

 _L also upon the strata over which they flow. Thus the 

 Medina, in the Isle of Wight, is a very narrow stream 

 while in the chalk district, but widens otit immediately 

 on reaching the less permeable Eocene beds. Indeed, 

 limestone districts can frequently be traced on a map by 

 the absence of streams and rivers. The Thames affords a 

 striking illustration of this influence of geological structure 

 upon the discharge of rivers. In flowing over Lias clay, it 

 is estimated to discharge 320 cubic feet per minute, but 

 coming to the porous Oolitic strata, its discharge suddenly 

 falls as low as 10 cubic feet per minute. 



The quality of the water is also influenced by the com- 

 position of the rocks through which the river flows ; and 

 considering the large amount of irrigation which is carried 

 on in many agricultural districts, the composition of river 

 w ater is of tin; first importance to the farmer. Thus, in 

 Surrey, the water of the ]Mole is far superior to that of the 

 Wey for irrigation purposes, for the ilole, after traversing 

 the Weald, flows through calcareous strata, and becomes 

 impregnated with fertilizing mineral substances ; while the 

 Wey flows almost entirely through barren sandy districts. 

 Tlie water from the Lower Greensand of Surrey is also ill- 

 adapted for irrigation on account of the very small amount 

 of mineral nuxtter dissolved in it ; nor is it a matter of any 

 surprise that the Lower Creensand itself sliould form here 

 so barren a soil, considering tlie small amount of soluble 

 material which it yields. The water from the Carboniferous 

 limestone of Yorkshire, on the other hand, is known to be 

 extremely useful as a fertilizing agent ; while the remark- 

 able excellence of the water-meadows of Gloucestershire is 



