VOL. LXXI.] PHILOSOPHICAL TRANSACTIONS. ly 



from the red colour of the nitrous acid when nitrous air and dephlogisticated air 

 are mixed together. Hence also mercury precipitated from its solution in any 

 acid, even by fixed alkalis, constantly retains a portion of the acid to which it 

 was originally united, as Mr. Bayen has shown ; so also does the earth of alum, 

 when precipitated in the same manner from its solution ; and thus several anoma- 

 lous decompositions may be explained. Indeed, I have reason to doubt whether 

 mercury does not attract acids more strongly than alkalis attract them. 



4thly. That concentrated acids are, in some measure phlogisticated, and 

 evaporate by union with fixed alkalis. 5thly. That knowing the quantity of 

 fixed alkali in oil of tartar, we may determine the quantity of real pure acid in 

 any other acid substance that is difficultly decomposed, as the sedative acid, and 

 those of vegetables and animals; for 10.5 gr. of the mild alkali will always be 

 saturated by 3.55 gr. of real acid: and reciprocally, the quantity of acid in any 

 acid liquor being known, the quantity of real alkali in any vegetable alkaline 

 liquor may be found. 



Of the specific gravity of Jived air in its fixed stale. — Being desirous to 

 know the specific gravity of some substances which are difficultly procured, or 

 at least preserved for any time, free from fixed air, such as fixed and volatile al- 

 kalis, I was induced to seek the specific gravity of the former in its fixed state, 

 as of an element necessary to the calculation of the latter ; it being very evident 

 that its density, in its fixed state, must be very different from that which it pos- 

 sesses in its fluid elastic state. I therefore took a piece of white marble, of the 

 purest kind, which weighed 440.25 gr. and weighing it in water, found it to 

 losel62gr. ; its specific gravity was therefore 2.7 J 75. Of this marble, reduced 

 to a fine powder, I put 1 80 gr. into a phial, and expelling the fixed air by the 

 dilute vitriolic acid and heat, I found its quantity amount to 105.28 cubic inches ; 

 the thermometer being at 65°, and the barometer between 29 and 30 inches; 

 this bulk of air would, at 55° of Fahrenheit, occupy but 102.4 cubic inches; at 

 which temperature, accordir o to the experiment of Mr. Fontana, a cubic inch 

 of fixed air, the barometer being at 29°^-, would weigh 0.57 of a grain ; there- 

 fore the weight of the whole quantity of fixed air amounted to 58.368 gr. which 

 is nearly -i- of the weight of the marble. At this rate, 100 gr. of the marble 

 contained 32.4 2 of fixed air. 



To determine the proportion of water and calcareous earth, and also the 

 specific gravity of this latter, I put 300g.25 gr. of the same marble finely 

 powdered into a crucible, loosely covered ; the crucible and its contents, before 

 calcination, weighed 83Q4 gr. and after remaining 14 hours in a white heat I 

 found it to weigh 7067-5 gr. The weight of the crucible alone was 5384.75 

 gr. ; therefore the weight of the lime singly was 1 682.75 gr. The marble then 

 lost by calcination 1326.5 gr.; 180 gr. of the marble should then lose 79.343 



d 2 



