﻿Phenomena connected loith the Boiling of Liquids. 163 



pressure of the atmosphere is not a fixed term, but that many 

 circumstances cause it to vary ; that it is much more inconstant 

 in vessels of metal than in vessels of glass ; and that the action, 

 more or less direct, of the external air on the sides of the vessels, 

 especially when of metal, as upon the surface of the water, pro- 

 duce considerable changes in the degree of heat that it may 

 receive in boiling. As the construction of the thermometer 

 depends on the fixity of the boiling-point, it is not surprising 

 that thermometers made on this supposition, with the greatest 

 possible care, should not always agree." 



4. I have given these details at some length, because French 

 and English writers of authority assign to Gay-Lussac the merit 

 of Achard' s discoveries. Biot seems to have led the way in this 

 respect. Writing in 1816*, he says, in reference to the boiling 

 of water, "II y a aussi quelques differences dans le degre de 

 Pebullition selon la nature des vases que Ton emploie, et selon 

 celle des substances qui se trouvent melees a Feau, meme quand 

 elle ne peut les dissoudre. Cette remarque est due a M. Gay- 

 Lussac/'' 



5. The effect of insoluble substances on the boiling-point was 

 also first noticed by Achard, in 1784-j-. The water was boiled in 

 a glass vessel ; and when the mercury in the thermometer was 

 steady, a drachm of the solid to be tried was thrown in, and the 

 effect noted in tenths of a degree on Reaumur's scale. When the 

 temperature had again become steady, a second drachm of the 

 substance was thrown in, and so on until no further effect was 

 apparent. A large number of substances were tried in this 

 way, and the results are given in Tables occupying fourteen 

 quarto pages. Each Table contains six columns, for recording 

 the name of the substance, the height of the barometer, the 

 boiling-point of the water before the addition, the weight of the 

 water, the weight of the substance added, and, lastly, the effect 

 on the thermometer in tenths of a degree Reaumur. Thus 1 

 drachm of iron-filings lowered the thermometer ten tenths, or 

 — ■ 10 as Achard writes it ; a second drachm had no further effect ; 

 copper-filings —8, tin-filings —13, white sand to —3, calc- 

 spar —13, quicklime —9, rosewood —11, limestone in powder 

 — 13, the same in a lump —3, bismuth in powder —12, the 

 same in fragments —8, and so on. Achard does not pretend to 

 offer any satisfactory explanation of these results, but he di- 

 stinctly claims the merit of having originated them. 



6. The effect of soluble substances on the boiling-point was 



* Traite de Physique, vol. i. p. 42. 



f Berlin Memoirs, 1784, published 1786. The following is the title of 

 the memoir :— " Sur l'effet produitpar 1'addition de differens corps a l'eau, 

 relativement au degre de chaleur dont elle est susceptible dans l'ebullition." 



M2 



