^iven on a late Trial. 329 



Upon my cross-examination, Mr. Scarlett made some in- 

 quiries respecting an experiment on old oil, to which I gave 

 the following reply : — 



" With new oil I did not observe any inflammable vapour 

 until the oil was heated to 586° ,• but the gas * from the old 

 oil was inflammable at 508°.'* " Suppose/* said he, *' there is 

 one gallon of oil that has been heated for every day in a week, 

 and allowed to cool again, and another heated for a month 

 every day, and allowed to cool again ; are you able to inform 

 the jury, which of the two would come to a certain degree of 

 temperature with the smallest degree of heat ?'* To this I re- 

 plied, " that I had made no experiment of that sort, but that I 

 had observed a remarkable thing respecting the evolution of 

 gas ; namely, that when the oil was heated to 590° it gave out 

 eight cubic inches of gas only in four minutes, but when heated 

 to 620° it gave out thirty-two cubic inches in one minute t-" 

 On being asked, if the sugars were heated to any thing like those 

 temperatures, what would be the effect on the sugar ? I replied 

 that " the sugar would be carbonized long before, and if heated 

 only to 400° it must have boiled over, unless the man had or- 

 dered the communication with the pump to be cut off." And, 

 it appears to me, that this is the great advEuitage of Mr. Wil- 

 son*s apparatus ; because, where there is any apprehension of 

 the sugar boiling over, the man has only to order the pump to 

 be stopped, and there is an end of the danger. 



Observations. — In some late experiments I have discovered 

 that the vapour of whale oil will burn readily at the surface of 



• In this part of my examination, the terms vapour and gas were used 

 indiscriminately, which was certainly improper ; but at that time I imagined 

 that the emanation which took fire as it issued from the heated oil at the 

 above temperatures, was a mixture of oil-vapour and carburetted-hydrogen- " 

 gas ; whereas, subsequent experiments have convinced me that no inflam- 

 mable gas is produced until a portion of the oil becomes actually decom> 

 posed, and charcoal formed. 



1 1 have no doubt but the gas, in both instances, was carbonic acid gas ; 

 for when cooled, and mixed with atmospheric air, it would not inflame on 

 the application of a match. 



Vol. X. Z 



