334 On the Chemical Evidence 



house ;" " that fat oils cannot be raised in distillation without 

 becoming totally changed, and therefore they are called Jixed 

 oils ; that it requires particular management, and a great deal 

 of heat, to produce the oil of dippel ;" that " he considered 

 the gas from the lamps used in the manufactory, was ten times 

 more dangerous than the oil apparatus •/' that " he had examined 

 the oil-vessel after the conflagration," and " not the least fis^ 

 sure, or symptom of explosion, was visible in it/' 



Observations. — The oil of dippel was introduced by Mr. 

 Allen, in consequence probably of its having been asserted that 

 this inflammable substance might have been produced by the 

 oil at Whitechapel, and have occasioned the conflagration. 

 Among all the hypothese's which have been advanced respect- 

 ing the fire at Messrs. Severns', this is the least tenable, as it 

 requires a red heat to convert fixed oil into dippel's oil. The 

 common mode of obtaining it for the purposes of medicine 

 is by the distillation of dri/ bones in an intense heat. 



At the close of this gentleman's examination, I was called to 

 explain to the jury the distinction between fixed and essential 

 oils ; and in answer to several questions, I stated, that '^ fat 

 oils, such as linseed oil, whale oil, olive oil, rapeseed oil, and 

 several others, are called Jixed oils, because they will endure 

 a high temperature, and may be boiled in an open vessel with 

 very little danger ; that they are also called fixed oils, to 

 distinguish them from essential oils, which cannot be heated 

 without danger * ; in short, there are no two substances in na- 

 ture," said I, " more different than fixed oils and volatile oils ; 

 they are alike only in name, and ought not to be confounded to- 

 gether." 



Mr. Thomas Barry was the next practical chemist who 

 was called. He stated that " he had made a few experiments, 



* I took this opportunity of saying a few words upon essential oils, be- 

 cause 1 had just been told there was an intention of insisting upon the 

 danger of distilling the essential oil of turpentine, which has nothing to 

 do with the question at issue, but was very likely, without explanation, to 

 have perplexed the jury. 



