VOL. LXXIV.] PHILOSOPHICAL TRANSACTIONS. 571 



tion, that the alkali employed to saturate the phlogisticated nitrous acid, was 

 always that of tartar which is partly mild ; and I have not examined whether 

 highly phlogisticated nitrous acid can perfectly expel fixed air from an alkali, 

 though I know no fact which proves the contrary. It should also be examined, 

 whether the same quantity of real nitrous acid is requisite to saturate a given 

 quantity of alkali, when the acid is phlogisticated, as is necessary when it is de- 

 phlogisticated. 



XXVII. An Attempt to Compare and Connect the Thermometer for Strong 

 Fire, described in Vol. 72 of the Philos. Trans, with the Common Mercurial 

 Ones. By Mr. J. Wedgwood, F.R.S. p. 358. 



This thermometer has now been found, from extensive experience, both in 

 my manufactories and experimental inquiries, to answer the expectations I had 

 conceived of it as a measure of all degrees of common fire above ignition : but 

 at present it stands in a detached state, not connected with any other, as it does 

 not begin to take place till the heat is too great to be measured or supported by 

 mercurial ones. What is now therefore wanting, to give us clear ideas of the 

 value of its degrees, is, to connect it with one which long use has rendered 

 familiar to us ; so that if the scale of the common thermometer be continued 

 indefinitely upwards as a standard, the divisions of mine may be reduced to that 

 scale, and we may thus have the whole range of the degrees of heat brought into 

 one uniform series, expressed in one language, and comparable in every part, 

 from the lowest that have hitherto been produced by any artificial freezing mix- 

 tures, up to the highest that can be obtained in our furnaces, or that the mate- 

 rials of our furnaces and vessels can support. 



The hope of attaining this desirable and important object gave rise to the 

 present experiments. This attempt is founded on the construction and applica- 

 tion of an intermediate measure, which takes in both the heats that are mea- 

 surable by the mercurial thermometer, and a sufficient number of those that 

 come within the province of mine to connect the two together ; the manner of 

 doing which will be apparent from the first 3 figures 11, 12, 13, pi. 7 ; where 

 f represents Fahrenheit's thermometer, with a continuation of the scale ; w my 

 thermometer ; and m the intermediate measure divided into any number of equal 

 parts at pleasure. 



For if the heat of boiling water, or 212 degrees of Fahrenheit, be communi- 

 cated to m, and its measure on m marked as at a; and if the heat of boiling 

 mercury, or 600° of Fahrenheit, be also communicated to m, and marked as at 

 b ; it is plain, that the number of degrees on m between a and b will be equal 

 to the interval between 212 and 600, that is, to 388° on Fahrenheit. In like 

 manner, by exposing m to 2 different heats above ignition along with my ther- 



4 d 1 



