360 On the Use of the Heat of Steam , 



for the present make only one observation on the prob- 

 able cause of the acceleration of the formation of soap, 

 which we observed. I believe that this acceleration is 

 due in great measure, if not entirely, to a motion of a 

 peculiar kind in the mixture of oil and lye, occasioned 

 by the sudden condensation of the steam introduced 

 into the liquor. It is a sharp stroke, like that of a 

 hammer, which made the whole apparatus tremble. 



These strokes, which succeeded rapidly in certain cir- 

 cumstances, and which were violent enough to be heard 

 at a considerable distance, must necessarily have forced 

 the particles of oil and alkali to approach each other, 

 and consequently to unite. 



As the violence of these strokes diminished greatly as 

 soon as the liquid had acquired nearly the temperature 

 of the steam, I propose to supply this defect by a par- 

 ticular arrangement of the apparatus in the experiment 

 we are going to make. I shall divide the vessel into 

 two parts, by a horizontal diaphragm of thin sheet cop- 

 per, and, causing a slow current of cold water to pass 

 through the lower division or compartment of the ves- 

 sel, I shall introduce steam into it, through a particular 

 tube destined for that purpose, as soon as the mixture 

 of oil and alkali which occupies the upper division of 

 the vessel is become too hot for condensing the steam. 



The steam which enters the water (always kept cold) 

 that fills the lower compartment of the vessel will be 

 condensed suddenly, and the sharp strokes which result 

 will be communicated through the thin diaphragm to 

 the hot liquid contained in the upper division of the 

 vessel, and will, I expect, accelerate the union of the 

 oil with the alkali. I shall then shut almost entirely 

 the cock which admits steam into the upper division of 



