504 PARAFFIN 



consequently crude-oil making docs not flourish in this, for three years, once busy 

 centre. The Flintshire refiners now look to Scotland for the raw material of their 

 manufacture. Many ingenious retorts designed specially to use cannel, some of which 

 were fully described in a previous edition, are now abandoned. 



In the extraction of crude oil, the cannel or shale has to be enclosed in a suitable 

 vessel, subjected to the degree of heat necessary to drive off its condensible vapours, 

 which vapours must pass through an outlet communicating with a suitable condensing 

 apparatus. 



This is simple enough ; and, for the mere production of paraffin oils from cannel or 

 shale, any kind of pot with an outlet-pipe, heated sufficiently by any kind of fire, will 

 suffice ; but to produce the maximum quantity of condensible vapours, and the mini- 

 mum quantity of incondensible gas, with the greatest degree of rapidity, and with the 

 smallest amount of outlay in plant, labour, and fuel, is a problem of some practical 

 difficulty. 



At first sight, the distillation of crude oil from cannels and shales appears almost 

 identical with gas-making, and, accordingly, the early retorts were simply copies of 

 those found by experience to be most suitable for gas-making. 



It soon became understood, however, that some of the most important conditions 

 to be observed are exactly the opposite of those upon which success in gas-making 

 depends. In gas-making the desideratum is to obtain the maximum amount of per- 

 manently elastic gas, and the minimum of condensible vapours ; in oil-making, we 

 require to reduce the permanent gases to the minimum, or, if possible, to make 

 none, and to obtain in their place the greatest possible quantity of condensible 

 vapours. It is now well known that if these condensible vapours are exposed to 

 a high temperature they are decomposed, and to a considerable extent converted 

 into permanent gas, and that the proportion of permanent gas bears some relation 

 to the excess , of temperature; the greater the heat, the more incondensible gas and 

 the less condensible vapours are formed. In gas-making, therefore, a very high tem- 

 perature is desirable ; in oil-making the great object is to subject the coal to no excess 

 of temperature beyond that which is absolutely necessary for its distillation into con- 

 densible vapours. 



Without dwelling further on obscure theoretical considerations, we may state 

 generally that the practical result of excessive heat is, besides a wasteful produc- 

 tion of permanent gas, the production of a crude oil of darker colour, higher specific 

 gravity, and possessing a characteristic odour well known to practical oil-makers as 

 that of ' burnt oil.' This burnt crude oil contains less solid paraffin, and is much 

 more difficult to refine than crude oil made at a lower temperature from like material. 

 It requires much more acid treatment, and even then produces burning-oil, which 

 still retains the ' burnt' odour, and blackens the lamp-glasses. 



The difficulties standing in the way of distillation at the proper temperature are : 

 1, the necessity of decomposing before distillation ; 2, the varying boiling-points 

 of the different products ; 3, the law of radiation, which demands a higher tem- 

 perature in the retort than that of coal ; and 4, the commercial necessity bf rapid 

 working. 



We will consider these seriatim ; and, in describing the improvements and 

 attempted improvements in retorts, refer each to the difficulty that it aims to over- 

 come : 



1. Although these hydrocarbons known as paraffin oils and paraffin are obtained 

 from the cannel by distillation, it is quite clear that they do not exist there as such. 

 We may saturate a mass of the porous cannel coke with these hydrocarbons, or with 

 crude solid paraffin, and produce a flaming coal thereby, which, upon careful distilla- 

 tion, will give back the volatile hydrocarbons ; but this artificially-saturated coke is 

 essentially different from the original cannel, as shown by the fact that we may remove 

 the hydrocarbon from the saturated coke by pounding it and washing with a solvent 

 of paraffin, &c., while the cannel itself resists the action of all such solvents. The 

 same is the case with Boghead and paraffin shales generally, though they are not 

 unfrequently described as porous minerals merely saturated with bituminous matter 

 by infiltration. Mr. GellaUey of Bathgate proved this experimentally by converting 

 paraffin into anthracene and naphthaline by passing its vapours through a red-hot 

 tube. 



The distillation of cannels and shales is thus a more complex process than the 

 distillation of a volatile oil, a resin, or bitumen. In the latter case the substance is 

 merely raised to its boiling-point, and this heat being maintained its vapour is driven 

 off. In the distillation of coal, the first function of the heat is to overcome the 

 chemical affinities which hold the hydrocarbon elements in the peculiar form in which 

 they exist in the coal, and then after this separation to drive their vapours over. It 

 js a compound process of decomposition and distillation, and the heat has to overcome 



