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♦ KNOWLEDGE ♦ 



[Nov. 9, 1883. 



in water ; if, however, it is thus treated with strong alcohol, 

 the casein becomes difficult of solution, or even quite in- 

 soluble. Alcohol added to solid soluble casein renders it 

 opaque, and gives it the appearance of coagulated albumen. 

 The alcohol itself dissolves a little of this. 



The characteristic coagulation of casein, or its conversion 

 from the soluble to the insoluble form, is produced rather 

 mysteriously by rennet. Acids precipitate it from an 

 aqueous solution, producing an apparent coagulation, but 

 it is not a true and complete coagulation like that eflfected 

 by the rennet, for on neutralising the acid precipitant with 

 an alkali or metallic oxide the casein again dissolves. 

 Excepting in the cases of acetic and lactic acids (vinegar 

 and the acid of sour mUk), which precipitate pure casein, 

 the acid precipitates appear to be a compound of casein 

 with the acids, and the casein is set free in its original 

 state when the acid goes over to the alkali or basic metallic 

 oxide. The action of rennet in the coagulation of casein is 

 still a chemical mystery, especially when we consider the 

 smallness of the quantity of coagulating agent required 

 for the rapid and complete conversion. 



A calf has four stomachs, the fourth lieing that which 

 corresponds to ours, both in structure and functions. It is 

 lined with a membrane from which is secreted the gastric 

 juice and other fluids concerned in effecting the conversion 

 of food into chyme. A weak infusion made from a small 

 piece of this " mucous membrane " will coagulate the 

 casein of two or three thousand times its own quantity of 

 milk, or the coagulation may be effected by placing a small 

 piece of the stomach (usually salted and dried for the 

 purpose) in the milk, and warming it for a few hours. 



Many theoretical attempts have been made to explain 

 this action of the rennet. Simon and Liebig supposed that 

 it acts primarily as a ferment, converting the sugar of milk 

 into lactic acid, and that this lactic acid coagulates the 

 casein ; but Selmi has shown that alkaline milk may be 

 -coagulated by rennet in the course of ten minutes, and 

 that after the coagulation it still has an alkaline reaction. 

 This is the case whether fresh naturally alkaline milk is 

 v^ed, or milk that has been artificially rendered alkaline by 

 the addition of soda. 



Casein, when thoroughly coagulated by rennet, then puri- 

 tied and dried, is a hard and yellowish horn-like substance. 

 It softens and swells in water, but does not dissolve therein, 

 nor in alcohol nor weak acids. Strong mineral acids 

 decompose it. Alkalies dissolve it readily, and, if concen- 

 trated, decompose it on the application of heat. When 

 moderately heated, it softens and may be drawn into threads, 

 and becomes elastic ; at a higher temperature it fuses, 

 swells up, carbonises, and develops nearly the same pro- 

 ducts of distillation as the other protein compounds. 



I have good and sufficient reasons for thus specifying 

 the properties of this constituent of food. I regard it as 

 the most important of all that I have to describe in con- 

 nection with my subject — the science of cookery. It 

 contains (as I shall presently show) more nutritious 

 material than any other food that is ordinarily obtainable, 

 and its cookery is singularly neglected, is practically an 

 unknown art, especially in this country. We commonly 

 eat it raw, although in its raw state it is peculiarly indiges- 

 tible, and in the only cooked form familiarly known among 

 us here, that of a Welsh rabbit, or rarebit, it is too often 

 rendered still more indigestible, though this need not be 

 the case. 



Here, in this densely populated country, where we 

 import so much of our food, cheese demands our most pro- 

 found attention. Tlie difficulties and cost of importing all 

 kinds of meat, fish, and poultry are great, while cheese may 

 be cheaply and deliberately brought to us from any part of 



the world where cows or goats can be fed, and it can be 

 stored more readily and kept longer than other kinds of 

 animal food. All that is required to render it, next to 

 bread, the staple food of Britons is scientific cookery. 



If I shall be able, in what is to follow, to impart to my 

 fellow-countrymen, and more especially countrywomen, my 

 own con\-ictions concerning the cookability, and consequent 

 improved digestibility, of cheese, these papers will have 

 " done the State some service ! " 



A CORRESPOXDEXT sends from the " Casket of Literary 

 Gems," Horace Smith's "Astronomical Alderman." The 

 following lines may amuse some of our readers who have 

 not seen the original. 



Then he began with mighty bonhomie 



To talk astronomy. 



" Sir," he exclaim'd between his bumpers, 



" Copernicus and Tycho Brahe, 



And all those chaps have had their day ; 

 They 're written monstrous lies, sir, — thumpers ! 

 Move round the sun ? — it's talking treason ; 

 The earth stands still — it stands to reason. 

 Round as a globe ? — stuff — humbug — fable ! 

 It's a flat sphere, like this here table, 

 And the suu overhangs this sphere, 

 Ay — just like that there chandelier." 

 " But," quoth his neighbour, " when the sun 

 From East to West his course has run. 

 How comes it that he shows his face 

 Next morning in his former place ■' " 

 " Ho ! there's a pretty question, truly 1 " 

 Replied otu- wight with an unrulj- 

 Burst of laughter and delight, 



So much his triumph seem 'd to please him ; 

 ** Why, blockhead, he goes back at night. 



And that 's the reason no one sees him." 



Teutu Stkasger thax Fiction. — A good joke is often 

 spoilt by dwelling too long upon preliminaries, and we shall 

 therefore avoid discursiveness. In these days of school- 

 boards and science departments, of examinations and cer- 

 tificates, it is hard to realise the following ; — The Electrical 

 Power and Storage Company had occasion recently to lend 

 a secondary battery charged and ready for use. For the 

 carriage the railway authorities claimed 2 2s. Cd. The 

 battery was used and retirned, the railway authorities now 

 claiming 17s. Gd. A remonstrance was made as to the 

 excess of charge in one direction over that in the other, 

 which was met by the reply : Oh ! but the cells were fully 

 charged going, and returned empty, hence the difference in 

 the carriage. — Electrician. 



Trouve's Rheostat. — A very useful rheostat has been 

 devised by M. Trouve, the well-known Parisian inventor. 

 It consists of a German silver spring enclosed in a nickel- 

 plated tube, the spirals not being allowed to touch each 

 other, and insulated from the tube by a pasteboard sheath- 

 ing. Inside the spring is a rubbing contact formed of a 

 metal rod split into four parts, like the split plugs of a 

 resistance box. This rod is graduated in divisions. The 

 current enters at one end of the spring, traverses it, the 

 rubbing contact, and the graduated rod. When the rod is 

 deeply inserted into the spiral coU, the current only 

 traverses a few turns, and the resistance in circuit is very 

 small ; but when the rod is pulled out, the number of turns 

 inserted is considerable. The di%-isions on the scale tell 

 the number of turns in circuit The device is employed by 

 Trouv^ in connection with his polyscopes to regulate the 

 strength of current supplied by a small Plante accumulator. 

 The plan of splitting the rubbing contact is worthy of 

 attention by electricians. — Engineering. 



