OILS AND SPIRITS. ] 



UNDULATORY FORCES. LIGHT. 



The schist is heated in an iron retort, and then exposed 

 to a current of very hot steam. The steam carries over 

 all the volatile matters namely, the oils, the tar, and 

 the paraffins. These are condensed in a proper receiver ; 

 and the semi-solid tar and paraffine are afterwards dis- 

 tilled, and then purified by means of sulphuric acid and 

 oxide of manganese, or bichromate of potash. After 

 the residue has been washed with boiling water and 

 weak soda, it is distilled a secoud time; then cooled, 

 strained, and pressed. The last purification is effected 

 by heating it to a temperature of 400 with strong sul- 

 phuric acid. By this means, all foreign matters are 

 dt-stroyed; and when washed with boiling water and a 

 so'.ution of soda, it is allowed to set, and is then ready 

 for the market. 



Pure paraffine is obtained in the form of brilliant 

 silvery scales when it crystallises out of boiling alcohol ; 

 but the paraffine of commerce is an amorphous substance, 

 having the appearance of a very transparent wax. It is 

 entirely without odour, and it does not communicate a 

 greasy stain to paper. It is slightly flexible, and when 

 warm may be moulded into any shape. It melts at a 

 temperature of 110, and distils at a red-heat, un- 

 ch.-iir.jeJ. Ether, naphtha, the volatile and fixed oils, 

 re it very readily ; and it mixes freely with wax, 

 stearine, and the fatty acids. The light emitted from it 

 varies with the size of the wick : when a small plaited 

 wick is used the light is clear, brilliant, and free from 

 smoke ; but when the large cotton strands of wax 

 candles are employed, the flame is large, yellow, and 

 very smoky. The experiments which have hitherto been 

 made with this substance, in order to determine its illu- 

 minating power, are not sufficiently complete to enable 

 us to judge of its value ; but the candles which we have 

 burnt are consumed at the rate of from 1G6 to 185 grains 

 per hour ; and the light emitted has, weight for weight of 

 candle consumed, been exactly one-twelfth less than that 

 of sperm. 



LAMP-OILS AND SPIRITS. 



Classification. Oils are divided by chemists into two 

 kinds namely, fixed and volatile. The former commu- 

 nicate a permanently greasy stain to paper or cloth, and 

 the latter do not. Olive oil may be mentioned as an 

 example of one, and turjientiiio of the other. Again, 

 tin; fixed oils are subdivided into those which become 

 thick or gelatinous on exposure to the air (drying oils), 

 3 linseed and poppy ; and those which do not (fat oils), 

 s olive and sperm. The cause of this change will be 

 referred to directly ; but it may be remarked, in a gene- 

 ral way, that drying oils are not adapted for combustion 

 in lamps, on account of this disposition to become thick, 

 and so to clog the wick. 



The composition of oil is very much the same as that 

 of the solid fats or butters : they consist, for example, of 

 two or more ingredients ; namely, licpiiil oleine, which in 

 always present in very large proportion, as from 70 to 90 

 per cent. ; and solid margarine or itearine. In addition 

 to this, many of the animal oils, as sperm, whale, seal, 

 fish, <bc., contain a volatile fat, which gives them their 

 ;.-ir odour. In the case of whale and seal oils, this 

 is Killed phocenine. The relative proportion of the solid 

 and liquid constituents of different oils is subject to great 

 variation, and hence the difference in the property of 

 solidifying, or becoming thick during cold weather. It 

 must be stated, however, that all oils deposit a solid 

 tallow-like material when they are subjected to cold ; 

 ninl when this deposit is very considerable in amount, as 

 is the case with the oils of cocoa-nut, lard, olive, A T c. , 

 inch are not well adapted for burning in lamps unless 

 thev are im-d in rather warm places. 



The sources of oils are very extensive ; in fact, they are 

 found in txith kingdoms of nature. Animals yield to us 

 larl and tallow-oil, sperm, whale, porpoise, seal, walrus, 

 h rring, cod, ling, and other such oils; while vegetables 

 furnish us with the oils of almond, olive, rape, clz-i, 

 cocoa-nut, linseed, hemp, mustard, poppy, cotton, teal, 

 sewama or t'i','ilie, castor, &o. In the fonner case the 



oil is obtained either from the cellular tissue which lies 

 immediately beneath the skin, or else from the liver; 

 and in the latter it is procured from the fruit, or the 

 cotyledons of the seeds. 



The- modes of extraction vary with different circum- 

 stances ; so much so, that it is scarcely possible to give a 

 general description of the numerous processes adopted. 

 In the case of lard, tallow, and cocoa-nut oils, the solid 

 fats are slightly wanned, then enclosed in linen or horse- 

 hair bags, and submitted to enormous pressure a pressure 

 of from four hundred to six hundred tons. The common 

 fish-oils, as those of the herring, pilchard, and sprat, are 

 obtained by piling the fish into heaps or walls, and then 

 weighting them with stones. The oils from the livers of 

 fish, as the cod, skate, ling, &c., are procured by boiling 

 the livers and skimming off the oil, or else by crushing 

 and pressing, or by allowing them to putrefy, so that the 

 tissue may break up and let out the oil. The fat or 

 blubber of different species of whale, porpoise, seal, dol- 

 phin, walrus, <tc., is subjected to heat in iron vessels, 

 and then submitted to pressure; and, lastly, vegetable 

 oils are procured by first crushing the seeds, then enclos- 

 in,' the bruised mass in bags, and exposing to enormous 

 pressure: this is obtained either by hydraulic power, 

 by screws, or by wedges driven by heavy stamps. " Lin- 

 seed, rape-seed, poppy-seed, and other oliferous seeds," 

 as we are informed by Dr. Ure, "were formerly treated 

 for the extraction of their oil by pounding them in wooden 

 mortars with pestles shod with iron, set in motion by 

 cams driven by a shaft, turned with horse or water- 

 power; then the triturated seed was put into woollen 

 bags, which were wrapped up in hair-cloths and siimv/i-d 

 between upright wedges in press-boxes, by the impulsion j 

 of vertical rams, driven also by a cam mechanism. In 

 the best mills, upon the old construction, the cakes 

 obtained by this first wedge-pressure were thrown upon 

 the bed of an edge-mill, ground anew, and subjected to 

 a second pressure, aided by heat now as in the first case. 

 These mortars and press-boxes constitute what are culled 

 Dutch mills. They are still in very general use, both in 

 this i-oiinti-y and on the continent; and are by many 

 persons supposed to be preferable to the hydraulic pres- 

 sure." 



Sometimes the crushed seeds are exposed to the action 

 of heat and a little moisture during the operation of 

 pressing. This facilitates the flow of the oil, and conse- 

 quently makes the seeds yield a larger produce; but the 

 oil is never so good under these circumstances, as it con- 

 tains much colouring matter, together with mucila 

 vegetable mucus and sugar; all of which diminish the 

 combustibility of the oil, and render it veiy liable to be- 

 come rancid. In the former case the oil is said to be 

 cold drawn, and in the latter hot. The amount of oil 

 obtained in this manner varies with different seeds, and 

 even with the same seeds in different countries and sea- 

 sons. Walnuts and hazel-nuts usually furnish about 

 half their weight of oil ; poppy seeds, nearly half ; olives, 

 about one-third ; rape-seed, a third ; and that variety 

 named colza, about two-fifths; hemp-seed, a fourth; al- 

 inonds, a fourth; Unseed, from one-fourth to one-fifth; 

 and the needs of grape, or wine-stones, about one-tenth. 



Olives are sometimes allowed to ferment, so as to 

 come soft and pulpy before they are crushed and ].n 

 In this way they yield a larger proportion of oil ; but the 

 oil is not good, and is only fit for lamps or machinery. 



We shall take occasion to notice more particularly the 

 details of all these processes when we come to the subject 

 of the individual oils. 



Refining nr 1'nrifijing. In the state in which oils are 

 first obtained from plants and animals, they always con- 

 tain impurities, as albumen, vegetable mucus, colouring 

 matter, sugar, ram-id acids, <tc. These must be removed 

 before the oil is fit for combustion in lamps ; and several 

 processes are adopted for this purpose. Sometimes the 

 oil is merely exposed to the action of steam or boilim; 

 water; and, after having been well agitated therewith, it 

 is allowed to stand until the oil floats to the surface in a 

 clear or pellucid condition : it is then drawn off by means 

 of a syphon or tap, and so separated from the water 



