340 HYPO-SULPHURIC ACID. 



2. Properties. 



(a.) Generally soluble in water, and have a bitter taste ; precipi- 

 tate nitrate of silver and mercury black, in the form of sulphurets of 

 those metals ; salts of lead and baryta are thrown down as white in- 

 soluble hypo-sulphites of those bases. 



(6.) Muriate of silver, recently precipitated, is dissolved by the 

 hypo-sulphites, and especially by that of soda, and a fluid is formed 

 sweeter than honey, and entirely void of metallic taste. The hypo- 

 sulphite of ammonia forms with muriate of silver, a white salt of which 

 1 grain imparts a perceptible sweetness to 32,000 grains of water.* 



HYPO-SULPHURIC ACID. 



1. Discovery. In 1819, by Welter and Gay-Lussac.f 



2. Preparation. Black oxide of manganese in fine powder, is 

 suspended in water, and a stream of sulphurous acid gas passed 

 through ; two acids are formed by the oxygen of the manganese ; 

 the sulphuric and hypo-sulphuric, and both unite with the base, form- 

 ing sulphate and hypo-sulphate of manganese ; both are decomposed 

 by adding solution of baryta slightly in excess, which precipitates 

 manganese and sulphate of baryta, and leaves hypo-sulphate of baryta 

 in solution. Carbonic acid gas is then passed through, to remove 

 any excess of baryta ; the solution is boiled to expel the carbonic 

 acid, and by evaporation, hypo-sulphate of baryta is obtained in crys- 

 tals. To a solution of these crystals, sufficient sulphuric acid is cau- 

 tiously added to saturate the baryta, which is precipitated in the form 

 of sulphate, and the hypo-sulphurous acid remains in solution. 



3. Properties. 



(a.) A colorless, inodorous acid, changes the test fluids ; concen- 

 trated by heat, or under the receiver of the air pump, its sp. gr. is 

 1.347, but if attempted to be carried farther, especially by heat, it is 

 decomposed and converted into sulphurous and sulphuric acids. 



(6.) Suffers no change from the air or from nitric acid ; it dis- 

 solves zinc like the stronger acids, and forms hypo-sulphate of zinc, 

 while hydrogen gas is evolved. 



(c.) It forms soluble salts with baryta, strontia, lime, lead, and 

 silver, which completely distinguishes it from sulphuric acid. 



4. Composition. Ascertained by decomposing the hypo-sulphate 

 of baryta by heat, and the proportion of sulphur appears to be 1=32, 

 and of oxygen, 5=40=72, for its equivalent. 



HYPO-SULPHATES. 



1. Preparation. Formed by direct combination with bases. 



* For numerous additional particulars, see Ann. de China. Vol. LXXXV ; Edin. 

 Philos. Jour. Jan. 1819, Vol. 1, 8, and 396, and Ure's Diet. 2d Ed. p. 97. 

 t Ann. de Chim. et de Phys. Vol. X. 



