84' Mr. H. C. Sorby on the Expansion of Water and 



It will thus be perceived that from 30° to 100° the agreement 

 is on the whole sufficiently close ; for the differences obey no de- 

 finite law, as if due to errors of observation. Below 30°, how- 

 ever, there is a most decided gradual increase in the dififei'ence, 

 evidently owing to a relative expansion taking place as the tem- 

 perature decreases. 



Since, then, for temperatures between 30° and 100° the volume 

 can be expressed with very considerable accuracy by means of 

 one simple formula, I was very anxious to ascertain whether the 

 law would hold good up to a much higher temperature ; for, in 

 that case, it would not only be much more simple than any 

 formula involving higher powers of t, but could be applied to 

 the object I had especially in view, since it would enable us to 

 deduce the temperature from the observed volume by solving the 

 formula as a quadratic equation, which of course could not be 

 done if it were essentially requisite to take higher powers into con- 

 sideration. I was not able to carry on the experiments at a higher 

 temperature than 200° C, because the water then begins to act 

 very powerfully on the glass tubes, and entirely decomposes 

 them in the course of time. At that heat the elastic force of the 

 vapour of water is very considerable, according to the experi- 

 ments of Dulong and Arago* being equal to 16 or 17 atmo- 

 spheres, or to about 240 lbs. to the square inch. It was there- 

 fore necessary to make use of glass tubes strong enough to 

 remove all fear of fracture and explosion ; and since it was also 

 far more desirable to determine the volume with moderate accu- 

 racy up to a very high temperature, than with great accuracy to 

 only a low temperature, I employed tubes of equal diameter for 

 their whole length, made from the tubing manufactured for 

 spirit thermometers, having an internal diameter of about g^pth 

 of an inch, and a thickness of glass equal to about j^th of an 

 inch. Having drawn out both ends of a portion about 2^ inches 

 long, so as to pass quickly into a capillary tube capable of being 

 sealed up with the blowpipe, it could be filled very easily, and 

 the liquid sealed up so as to leave a bubble of air about ^vA of an 

 inch long. I had thus a column of liquid of uniform width, 

 about 2 inches long, and a bubble of air, which could be made 

 to move to any part of the tube by violent swings of the arm ; 

 and by thus causing it to move to each end of the tube where 

 drawn out and of less width than the rest, and by making suit- 

 able measurements both then and when it was in that part where 

 the diameter was uniform, I was able to ascertain what would 

 have been the true length of the column of liquid, if the tube 

 had been of the same diameter for its whole length. 



In order to measure with great accuracy the length of the 

 • Quarterly Journal of Science, Jiiuuiuy to June 1830, p. 191. 



