240 PHILOSOPHICAL TRANSACTIONS. [ANNO 1782. 



: O.C093 ; but in reality these ] 6° of heat afforded a dilatation equal only to 

 0.0063; for 1.4650— 1.4587 = 0.0063; so that the difference between the 

 calculated and observed dilatations is only , „VW, a difference of no consequence 

 in the present case; and even that might arise from the immersion of the cold 

 glass ball filled with mercury in the liquor, it being the solid I use to try the spe- 

 cific gravity of liquids. In the next case the difference is still less; for 90 : 0.0527 

 :: 56 : 0.0327; but 56° of heat produced in reality a dilatation of 0.0348, for 

 1.4650 — 1.4302 = 0.0348, so that the calculation is deficient only by TrnrW- 



I afterwards tried another, and somewhat Deg. Sp. gravity. 



stronger, spirit of nitre, whose specific gravity 4g ' 1*653 



was, at 150 1.3792 



Here also the expansions are nearly proportional to the degrees of heat; for ] 16 

 of heat (the difference between 34 and 150) produce an expansion of O.O958; 

 and 15° of heat (the difference between 34 and 49) produce an expansion of 

 O.OO97, and by calculation 0.0123, which last differs from the truth only by 

 1 » 6 o • By this experiment we see, that the stronger the spirit of nitre is, the 

 more it is expanded by the same degree of heat: for if the spirit of nitre of the 

 last experiment were expanded in the same proportion as in the first, its dilata- 

 tion by 1 l6° of heat should be O 0679, whereas it was found to be O.0958. 



As the dilatation of spirit of nitre is far greater than that of water by the same 

 degree of heat, and as it consists only of acid and water, it clearly follows, that 

 its superior dilatability must be owing to the acid part; and hence the more acid 

 is contained in a given quantity of spirit of nitre, the greater is its dilatability. 

 We might therefore suppose, that the dilatation of spirit of nitre was interme- 

 diate between that of the quantity of water it contains and that of its quantity 

 of acid; but there exists another power also which prevents this simple result, 

 namely, the mutual attraction of the acid and water to each other, which makes 

 them occupy a less space than the sum of their joint volumes, which condensa- 

 tion I have therefore called their accrued density. Taking this into the account, 

 we may consider the dilatation of spirit of nitre as equal to those of the quan- 

 tities of water and acid it contains, minus the condensation they acquire from 

 their mutual attraction, and this rule holds as to all other heterogeneous com- 

 pounds. 



To find the quantities of acid and water in spirit of nitre, whose specific gra- 

 vity was found in degrees of temperature different from those for which the table 

 was constructed, viz. 54, 55, or 56° of Fahrenheit, the surest method is to find 

 how much that spirit of nitre is expanded or condensed by a greater or less degree 

 of heat, and then, by the rule of proportion, find what its density would be at 

 55°; but if this cannot be done, we shall approach pretty near the truth, if we 



