132 



ON THE EXPANSION OF ELASTIC FLUIDS. 



Expansion of 

 common air. 



Intermediate 

 expanfion. 



the glafs tube, which was found to raife the thermometer, to 

 212°. Small fpecks of* white paint were put upon the diviiions 

 of the manometer together with numbers which were difcern- 

 ible through the. containing tube. For lower temperatures, 

 a deep tin veflel containing hot water was ufed, in which the 

 manometer was immerfed, the water being well agitated pre- 

 vioufly to each obfervation. 

 The conclufions From a great many experiments made in this way on com- 

 Berthollet ' fec^ mon a ' r ' an( * n kewife u P on hydrogenous gas, oxygenous and 

 are accurate; nitrous gafes, and carbonic acid gas, I can aflert that the con- 

 but thofe of dufjons of De Luc, Roi, Sauffure, Berthollet, &c. are nearly 



Morveau and du / 



Vernois not fo. accurate throughout, and that thole of de Morveau and du 



Vernois are extremely inaccurate in the higher temperatures. 

 I have repeatedly found that 1000 parts of common air of 

 the temperature 55° and common prefTure, expand to 1321 

 parts of the manometer ; to which adding 4 parts for the 

 correfponding expanfion of glafs, we have 325 parts increafe 

 upon 1000 from 55° to 212° ; or for 157° of the thermome- 

 tric fcale. As for the expanfion in the intermediate degrees, 

 which Col. Roi's experiments (hew to be a Jlowly diminijhing 

 one above the temperature of 57°, but which de Morveau's 

 on the contrary (hew to be a rapidly increajiiig one in the higher 

 part of the fcale; I am obliged to allow that Col. Roi is right, 

 though it makes in fome degree againft an hypothefis I have 

 formed relative to the fubjeel ; he has certainly however 

 made the diminution too great from 72° downwards, owing 

 to his not perceiving that he actually defiroj/ed a portion of the 

 claftic fluid he was operating upon (aqueous vapour) in redu- 

 cing its temperature fo low ; if his air had been previoufly 

 dried by fulphuric acid, &c. he would not have found fo re- 

 markable diminution below 72°. My experiments give for 

 77^° above 55°, 167 parts; for the next 77 {° only 158 parts; 

 and the expanfion in every part of the fcale feems to be a gra- 

 dually diminifhing one in afcending. 

 Other gafes The refults of feveral experiments made upon hydrogenous 



agree with com-g as ^ oxygenous gas, carbonic acid gas and nitrous gas, which 

 were all the kinds I tried, agreed with thofe on common air 

 not only in the total expaniion, but in the gradual diminu- 

 tion of it in afcending : the finall differences obferved never 

 exceeded 6 or 8 parts on the whole 325 ; and differences to 



this 



