Chap. II.] Chemical Philosophy. 133 



many experiments'*', lie produced an instrument 

 which he called a Pyrometer^ and which, by means 

 of the contraction oi day, marks, witli much pre- 

 cision, the different degrees of heat, from 947° of 

 Fahrenheit's scale, to the greatest heat of a wind- 

 furnace. 



It was first observed by Dr. Black, that dilTerent 

 bodies have different capacities for imbibing and 

 retaining heat. The fact was aftervvarfls noticed, 

 and the subject further investigated, by Drs. Irvine 

 and Crawford, and by professor Wilcke, of Stock- 

 holm. The last named gentleman called tlie quan- 

 tity of caloric necessary to raise the temperature of 

 substances a given number of degrees, their specific 

 heat. For measuring this heat an instrument was 

 contrived by Messrs. de la Place and Lavoisier, and 

 called by the latter a Calorimeter; the nature and 

 value of ^vhich may be seen in various books of 

 chemistry. 



Another instrument, invented in modern times, 

 and which has engaged much of the attention of 

 chemists, is the Eudiometer \. This instrument was 

 invented by Dr. Priestley, and is used for ascer- 

 taining the purity of the atmospherical air, or the 

 quantity of oxygen contained in it, which is indi- 

 cated by tlie diminution of its volume on being 

 mixed with nitrous air. Tiie discovery of this pro- 

 perty of nitrous gas, and the invention founded 

 upon it, soon gave rise to many attempts to \m- 

 prove on the principle, a!Y<l to contrive eudiome- 

 ters of a more elegant and advantageous kind, and 



* See Philosophical Tranmctions for 1/82, 1784, 1/86. 

 t See Additional NoU-s—(Xj. 



