254 On the VolalUUy and Infiammalility 



ever, was found very inconvenient, inasmuch as that part of the 

 sugar which was nearest the fire was burnt before the rest could 

 be brought to a proper temperature. Ingenious and scientific 

 men contrived to produce the requisite degree of heat by pipes 

 of boiHng water coiled and immersed into the syrup, or sugar. 

 But this difficulty arose, that the sugar would not boil at the 

 same heat as the water, and therefore a high pressure, attended 

 with much danger, was required. At Liverpool tallow was iu 

 common use for this purpose ; but this was found extremely of- 

 fensive, and, to obviate its inconveniencies, Mr. Wilson had in- 

 vented a process for using fixed oil. This oil was put into a large 

 retort, and from it a coil of pipes passed into the sugar whicii 

 it was intended to bring into a boiling state. The oil required 

 a temperature of 600 degrees of Fahrenheit for boiling, and sugar 

 350. This was a degree of temperature below any heat that 

 could create danger. The first question therefore would be, 

 whether by means of this communication there was any increase 

 of risk; and, secondly, whether the loss was occasioned thereby 

 — as he understood, instead of being increased, the risk was di- 

 minished, upon a comparison with the former mode. One of 

 the risks attending the former mode was that of the sugar boiling 

 over, in which case the premises must be infallibly destroyed. 

 Bv the new process, a thermometer was fixed in the retort, and, 

 as soon as the oil was heated to the degree of 350, it passed 

 into pipes which conveyed it through the sugar, till, like the cir- 

 culation of the blood, it reflowed into the retort. It would be 

 idle to suppose that, upon a question of this nature, he was not 

 aware of some of those grounds which would be taken on the 

 other side. It would be said, as he apprehended, that the pipes 

 might burst ; but this was guarded against by the valves being 

 smaller than the diameter of the pipe. But then it might be 

 urged, that gas must be created ; and to this he would reply, 

 that gas was not created by fixed oil until it arrived at a tem- 

 perature of between 600 and 700 degrees, long befoie which the 

 thermometer would have exploded. To be brought to such a 

 temperature, the heat must be continued for a long time in a 

 state of almost incredible intensity, for the accession of heat be- 

 came very slow after a certain point. From the retort a small 

 pipe ascended, for the purpose of carrying off such air as might 

 remain in the pij^es, and in a retort not always full. If any gas 

 was created, it must escape through this pipe. Again, it might 

 be urged, that the air might be driven downwards by a sudden 

 draught — a result, certainly, to be looked for in an ordinary room, 

 but, if admitted into these premises, would have defeated the 

 whole process which was carrying on. Every draught was care- 

 fully prevented, and the fire fed by external air admitted from 



behind 



