July 6, 188?.] 



♦ KNOWLEDGE ♦ 



they pass into a state of vapour, and these vapours when 

 cooled, recondense into their original form of liquid oil 

 without alteration. Hence they are called "volatile oils," 

 while the greasy oils which cannot thus be distilled (in 

 which animal fats are included), are called " fixed oils." 



A very simple practical means of distinguishing these 

 is the following : — Make a spot of the oil to be tested on 

 clean blotting-paper. Heat this by holding it above a 

 spirit lamp flame, or by toasting before a fire. If the oil 

 is volatile, the spot disappears ; if fixed, it remains as a 

 spot of grease until the heat is raised high enough to char 

 the paper, of which charring (a result of the dissociation 

 above-named) the oil partakes. 



But the practical cook may say " this is wrong, for the 

 fat in my frying-pan does boil, I see it boil, and I hear it 

 boU." The reply to this is, that the lard, or dripping, or 

 butter that you put into your frying-pan is oil mixed with 

 water, and that it is not the oil but the water that you see 

 boiling. To prove this, take some fresh lard, as usually 

 supplied, and heat it in any convenient vessel, raising the 

 temperature gradually. Presently, it will begin to splutter. 

 If you try it with a thermometer you will find that this 

 spluttering point agrees with the boiling point of water, 

 and if you use a retort you may condense and collect the 

 splutter-matter, and prove it to be water. So long as the 

 spluttering continues the temperature of the melted fat, 

 i.e., the oil, remains about the same, the water vapour 

 carrying away the heat. When all the water is driven oif 

 the liquid becomes quiescent, in spite of its temperature, 

 rising from 212° to near 400°, then a smoky vapour comes 

 off and the oil becomes darker ; this vapour is not vapour 

 of lard, but vapour of separated and reoombined con- 

 stituents of the lard, which is now sufiering dissociation, the 

 volatile products passing off while the non-volatile carbon 

 (i.f., lard-charcoal) remains behind, colouring the liquid. 

 If the heating be continued, a residuum of this carbon, in 

 the form of soft coke or charcoal, will be all that remains 

 in the heated vessel. 



We may now understand what happens when something 

 humid — say a sole — is put into a frying-pan which contains 

 fat heated above 212°. Water, when suddenly heated 

 above its boiling point is a powerful explosive, and may be 

 very dangerous, simply because it expands to 1,728 times 

 its original bulk when converted into steam. Steam-engine 

 boilers and the boilers of kitchen stoves sometimes explode 

 simply by becoming red-hot while dry, and then receiving a 

 little water which suddenly expands to steam. 



The noise and spluttering that is started immediately 

 the sole is immersed in the hot fat is due to the explosions 

 of a multitude of small bubbles formed by the confinement 

 of the suddenly expanding steam in the viscous fat from 

 which it releases itself with a certain degree of violence. 

 It is evident that to effect this amount of eruptive violence, 

 the temperature must be considerably above the boiling- 

 point of the exploding water. If it were only just at the 

 boiling-point, the water would boil quietly. 



As we all know, the flavour and appearance of a boiled 

 sole or mackerel are decidedly ditTerent from those of a 

 fried sole or mackerel, and it is easy to understand that 

 the diiler(!nt results of these cooking processes are to some 

 extent due to the difference of temperature to which the 

 fish is subjected. 



The surface of the fried fish, like that of the roasted or 

 grilled meat, is "browned." What is the nature, the 

 chemistry of this browning 1 



I have endeavoured to find some answer to this question, 

 that I might (juote with authority, but no technological or 

 purely chemical work within my reaih supplies such 

 answer. Rumford refers to it as essential to roasting, and 



provides for it in the manner already described, but he 

 goes no further into the philosophy of it than admitting 

 its flavouring effect 



I must therefore struggle with the problem in my own 

 way as I best can. Has the gentle reader ever attempted 

 the manufacture of " hard-bake," or " toffy," or " butter- 

 scotch," by mixing sugar with butter, fusing the mixture, 

 and heating further imtil the weU-known hard, brown con- 

 fection is produced. I venture to call this fried sugar. If 

 heated simply without the butter it may be called baked 

 sugar. The scientific name for this baked sugar is caramel. 



The chemical changes that take place in the browning of 

 sugar have been more systematically studied than those 

 which occur in the constituents of flesh when browned in 

 the course of ordinary cookery. Believing them to be 

 nearly analogous, I will state, as briefly as possible, the 

 leading facts concerning the sugar. 



Ordinary sugar is crystalline, i.e., when it passes from 

 the liquid to the solid state it assumes regular geometrical 

 forms. If the solidification takes place undisturbed and 

 slowly, the geometric crystals are large, as in sugar- 

 candy ; if the water is rapidly evaporated with agitation, the 

 crystals are small, and the whole mass is a granular aggre- 

 gation of crystals, such as we see in loaf sugar. If this 

 crystalline sugar be heated to about 320° F. it fuses, and 

 without any change of chemical composition undergoes 

 some sort of internal physical alteration that makes it 

 cohere in a different fashion. (The learned name for this is 

 allotropisiii, and the substance is said to be aUulrojnc, other 

 conditioned; or (^i7rto?y)Aic, two-shaped.) Instead of V^eing 

 crystalline the sugar now becomes vitreous, it solidifies as 

 a transparent amber-coloured glass-like substance, the well- 

 known barley sugar, which differs from crystalline sugar 

 not only in this respect, but has a much lower melting- 

 point ; it liquefies between 190^ and 212°, while loaf-sugar 

 does not fuse below 320". Left to itself, vitreous sugar 

 returns gradually to its original condition, loses trans- 

 parency, and breaks up into small crystals. In doing this, 

 it gives out the heat which during its vitreous condition 

 had been doing the work of breaking up its crystalline 

 structure, and therefore was not manifested as temperature. 



This return to the crystalline condition is retarded by 

 adding vinegar or mucilaginous matter to the heated sugar, 

 hence the confectioners' name of " barley sugar," which, in 

 one of its old-fashioned forms, was prepared by boiling 

 down ordinary sugar in a decoction of pearl barley. 



The French cooks and confectioners carry on the heating 

 of sugar through various stages bearing different technical 

 names, one of the most remarkable of which is a splendid 

 crimson variety, largely used in fancy sweetmeats, and 

 containing no foreign colouring matter, as commonly sup- 

 posed. Though nothing is added, something is taken away, 

 and this is some of the chemically-combined water of the 

 original sugar, in the parting with which not only a change 

 of colour occurs, but also a modification of flavour, as 

 anybody may prove by experiment. 



When the temperature is gradually raised to 420°, the 

 sugar loses two e(jui\alents of water, and becomes caramel 

 — a dark-brown substance, no longer sweet, but ha\nng a 

 new flavour of its own. It further diflers from sugar by 

 being incapable of fermentation. Its analogies to tlie 

 crust of bread and the " brown " of cooked animal food 

 will be further discussed in my next. 



According to Mr. Kolb, one of tlie secretaries of the 

 German Imperial Telegraph Department, the 127,166 

 galvanic cells in use cost .£12,3.")0, of which .£2,727, or 

 about 22 per cent., were recovered by the sale of the 

 battery residues, consisting of copper, zinc, and lead salts. 



