162 



♦ KNO^A^LEDGE ♦ 



[June 1, 1889. 



is ready and eager to burn by combining with oxygen ; in 

 the second, the thirst of the hydrogen for oxygen is already 

 satisfied ; it can take up no more, and is quite incombustible, 

 as we know to be its condition in water. 



Various methods of separating the glycerine have been 

 devised. The first practically carried out was the lime pro- 

 cess. About 10 cwt. of tallow or palm-oil was melted with 

 about 140 gallons of water, and to these were gradually 

 added about 100 gallons of milk of lime containing a 

 quantity of lime equal to about 14 per cent, of the weight 

 of the tallow. This mi.Kture was heated and stirred until 

 an insoluble soap was formed by the union of the fatty acids 

 with the lime ; the lime, being a stronger base than the 

 glycerine, took the acid away and liberated it, the glycerine 

 thus separated remaining dissolved in the yellowish liquor 

 standing above the soap, from which it was finally separated 

 and purified. 



The lime-soap formed by the combination of the lime 

 with the fatty acids is useless, but the fatty acids, having 

 but feeble chemical energy, are easily displaced by a stronger 

 mineral acid which combines with the lime and sets them 

 free. If sulphuric acid is used, solid gypsum is formed, 

 which settles down from the melted fatty acids, which are 

 run off and washed to remove remaining traces of sulphuric 

 acid and gypsum. 



When cooled, these fatty acids solidify into a solid of 

 crystalline structure commonly known as stearine, thus 

 named from one of its constituents, the stearic acid. Stearine 

 candles were made from this after pressing out the liquid 

 oleic acid which was used for soap-making. 



Other methods followed and superseded this, such as the 

 use of superheated steam to diminish the quantity of lime 

 I'equired, the use of concentrated sulphuric acid, and, better 

 still, the skilful application of the repulsive power of heat, 

 which, at a temjjerature of about 570° (or a little higher 

 when superheated steam is used as the heating medium), 

 effects the direct dissociation of the fatty acids from the 

 glyceiine, and thus separates them in nearly pure condition. 



Candles made of the stearine thus obtained are hard and 

 free from greasiness. They burn with a much whiter, 

 purer, and hotter flame than those made of tallow, one of 

 the incidental advantages of this being the full combustion 

 of the wick, as in wax and spermaceti candles (which are 

 composed cliiefly of the fatty acids), and therefore no snulfing 

 is required. 



Another and still more recent step in candle-making is 

 that of using paraffin, which is a natural hydrocarbon 

 obtained from the tarry oil that comes over when cannel 

 coal and certain bituminous shales are slowly distilled, or, 

 better still, from petroleum. This crude material is washed 

 with sulphui'ic acid, which carbonises any carbohydrates 

 that may be present by combining with their constituent 

 water, the carbon thus separated sinking to the bottom 

 as " acid tar," and is left behind when the mixture is 

 redistilled. 



A curious change is observable in the distillate thus 

 obtained. It is not only refined as regards colour (crude 

 petroleum is brown, and crude shale oil nearly black), but is 

 seen to contain pearly crystalline scales when cold, scales 

 that disa])pear when the temperature is raised. By lower- 

 ing the temperature considerably these scales are easily 

 separated by simply straining through suitable bags and 

 pressing the contents of the bags until the liquid oil is so far 

 run out as to leave a hard solid cake of the crystals behind. 

 These, when further refined by washing in light mineial 

 oil, constitute the beautiful substince that has received the 

 name of " paraffin " on account of its lack of chemical 

 affinity. It closely resembles spermaceti, and, mixed with a 

 little wax, is nearly equal to it as a mateiial for candles. 



Not long ago it was a chemical curiosity, now it is familiar 

 to everybody in the form of the beautiful candles that arc 

 retailed at fivepence per pound, less than the former cost of 

 the commonest tallow dips. These require no snuffing, but 

 are inconvenient in hot climates on account of the low melt- 

 ing point of their material. 



This defect was ominously displayed at a grand coronation 

 ball given in Mexico by the ill-fated Maximilian. The snloti 

 was lighted brilliantly with some hundreds of these candles 

 — then a novelty and imperfectly understood. As the 

 dancing proceeded and the room grew warmer and warmer, 

 the candles softened and bowed over, and streams of their 

 melted material poured down so disastrously upon the dresses 

 of the dancers that the ball was hastily terminated. 



In all respects but this tendency to " gutter," owing to 

 ready fusibility and the fluidity of the melted material, 

 these cheap candles are equal to the costly wax and sper- 

 maceti of the luxurious. Science here, as in other directions, 

 is foreshadowing the future course of human progress, 

 whereby, without any reduction of rational and beneficial 

 refinements and luxuries of the rich minority, the millions 

 gradually and peacefully approach nearer and nearer to a 

 general equality of partaking. 



THE OCCURRENCE OF GOLD. 



By 1). A. Louis, F.I.C, F.C.S. 



N considering the occurrence of gold, there are 

 two or three of its properties which it is useful 

 to bear in mind in order to account for the 

 unique position it holds in the mineral kingdom ; 

 these are : — its high specific gravity, the great 

 disinclination it exhibits to enter into combina- 

 tion with other elements, and the peculiarity 

 of its solubility. 



Most metals occur in natiu-e mineralised or combined with 

 various elements ; for instance, silver is found sometimes 

 free, but most frequently combined with sulphur as in silver 

 glance, also with arsenic or antimony and sulphur in 

 pyrargyrite and proustite, with chlorine in horn silver, and 

 with other elements. Lead is universally found combined 

 with sulphur and galena, also with carlionic acid as cerussite 

 or lead spar, and in other combinations ; tin, in its best known 

 ore, cassiterite, is combined with oxygen, whilst zinc in 

 blende is combined with sulphur, and in calamine with 

 carbonic acid. But gold is one of the few elements which 

 exist in nature free or uncombined, and with the exception 

 of its existence in comparatively small quantities, combined 

 with the rare element tellurium, it is always found in the 

 metallic state. Native gold, however, contains varying 

 pro])ortions of imjiurities, the impurity in most instances 

 being metallic silver, and perhaps copper ; therefore we can 

 dismiss the question of the chemical occurrence of gold with 

 the statement that it generally occurs in the free state 

 alloyed with more or less silver, and is sometimes found as 

 telluride. 



Turning to its mineralogical or petrological associations, a 

 very similar degree of simplicity awaits us, for gold is, with 

 few exceptions, found associated with the well-known non- 

 metallic mineral quartz, whilst iron pyrites is the most 

 general metalliferous mineral which accompanies gold, 

 although copper pyrites, galena, blende, and arsenical 

 pyrites ar^e frequently auriferous, and sooie dozen other 

 minerals are from time to time found to have particles of gold 

 mixed with them. The rocks in which gold is found are mostly 

 metamorphic, or those rocks which have in periods gone by 

 been deposited during the decay of pre-existing rocks, but 



