1826.] of Hyponitrous and Sulphuric Acids. 371 



nitrous gas, and an atom ofnitrous acid, into which the upper ones 

 are resolved by the transference of an atom of oxygen from the one 

 to the other. To confirm this explanation, it is necessary that 

 the proportion of nitrous gas to the nitrous acid obtained by 

 experiment, should agree nearly with the proportion of the equi- 

 valent of the former compound to the equivalent of the latter. 

 Now the proportion of 5*273 to 7'8 approaches so nearly the 

 proportion of 30 (the equivalent of nitrous gas), to 46 (the equiva- 

 lent ofnitrous acid), that we may consider the discrepancy as 

 arising from unavoidable errors of experiment, the fourth propor- 

 tional being in fact 44*37. 



Tlie crystalline solid which has been above described is pro- 

 bably identical with that obtained many years ago by MM. 

 Clement and Desormes (Ann. de Chimie, lix.33o), by mingling, 

 in a glass balloon, sulphurous acid, nitrous gas, atmospheric air, 

 and aqueous vapour ; and also with a similar compound, after- 

 wards formed by M. Gay-Lussac, by adding to sulphuric acid 

 the product of the distillation of nitrate of lead, which he consi- 

 ders as chiefly hyponitrous acid (Ann. de Chim. et de Phys. i. 

 407). It furnishes another example, in addition to those before 

 known, of a weak acid serving as a base to a more powerful one. 

 The combinations of fluoric acid with silica and with boracic 

 acid, are familiar instances; and M. Berzelius has lately disco- 

 vered others in the compounds of fluoric acid with the columbic, 

 titanic, tungstic, and molybdic acids. These, however, differ 

 from the compound of hyponitrous and sulphuric acids in 

 possessing greater permanency, so as to form with bases distinct 



fenera of salts, entitled to the names of fluo-titanates, fluo-colum- 

 ates, &c.; whereas the compound of sulphuric and hyponitrous 

 acids is instantly decomposed by contact with a base, and the 

 salts obtained are identical with those which would have been 

 formed if those acids had been separately united with the same 

 base. 



Article X. 



An Historical Sketch of Photometry, with Remarks. 

 By-the Rev. Baden Powell, MA. FRS. 



(To the Editors of the Annals of Fhilosophy.) 

 GENTLEMEN, ^pril 10, 1826. 



To possess some principle upon which to deduce at least 

 tolerably accurate measures of the absolute or relative illumi- 

 nating powers of different species of natural or artificial light, is 

 of no inconsiderable importance both in respect to many points 

 of scientific investigation, and to various questions of practical 

 and economical calculation. 



2 n2 



