394 Appendix. 



ed, by a moderate heat, into a substance somewhat resembling gum j 

 and, by weak chemical agents, into sugar. Among inorganic com- 

 pounds, we have a remarkable instance of the effects of heat, (raised 

 however to a higher degree,) in the change of phosphoric into pyro- 

 phosphoric acid. In most cases of this kind, it is probable that in- 

 creased heat produces no change, either in the number or proportions 

 of the atoms of the substances ; but that,, in some way which chem- 

 ical science has not yet prepared us to explain, it modifies only the 

 arrangement of the atoms, and thus confers new distinctive characters. 



In pursuing the inquiry experimentally, two circumstances seemed 

 to me to require to be established. 



1st, That raw cotton, and other substances likely to harbor conta- 

 gion, would sustain no injury by the temperature conceived to be ne- 

 cessary for their disinfection. 



2dly, That in at least some one unequivocal instance, contagious 

 or infectious matter should be proved, by actual experiment, to be 

 destructible at that temperature. 



I. To ascertain the first point, I submitted, in August, 1824, a 

 quantity of raw cotton to a dry temperature* of 190° Fahrenheit, 

 which was steadily kept up in the inner compartment of a double 

 vessel heated by steam, during two hours. When the staple of the 

 cotton was examined by Mr. Garnett, he pronounced it to be so es- 

 sentially injured, as to set at rest, on a first view, all intentions of 

 adopting this method of purification. The same unpromising ap- 

 pearance was presented also by cotton yarn, which, after being spun, 

 had been heated during two hours at 190° Fahrenheit. After being 

 allowed to cool during a quarter of an hour, it was compared with 

 yarn of the same fineness which had not been heated, with the fol- 

 lowing result : 



lbs. avoird. 



A hank of mule twist (40 to the pound) not heated, required 



a weight, to break it, of - - - - - - 246^ 



A hank of ditto, ditto, heated to 190° and just cooled, - I66f 

 The strength of the yarn, measured by its power of supporting 

 weights, had therefore suffered a diminution, by being heated, of 

 fully one-third. The remainder of the yarn so heated having been 

 laid aside in a cellar, was accidentally examined on the fourth day, 



* I use the expression dry temperature, in order that it may be distinctly under- 

 stood, that the cotton was not in contact with steam, wliich was used merely as the 

 vehicle of heat. 



