HYDROCHLORIC ACID 869 



tube, closed at one end, a little iodine, then a small quantity of rotighly-powdered glass 

 moistened with -water, upon this a few small fragments of phosphorus, and lastly more 

 glass ; this order, iodine, glass, phosphorus, glass, is repeated until the tube is two- 

 thirds filled. A cork and narrow bent tube are then fitted and gentle heat applied, 

 when the hydriodic acid is liberated, and may be collected in dry bottles by the dis- 

 placement of air. Another process is" to place in a small retort 10 parts of iodide of 

 potassium with 5 of water, add 20 parts of iodine, then drop in cautiously 1 part of 

 phosphorus cut into small pieces, and apply a gentle heat ; hydriodic acid will be 

 formed abundantly, and may be collected as before stated. The following equation 

 expresses the reaction : 



2KI + 51 + P + 8HO yield 2KO,HO,P0 5 + 7HI. 

 2X1 + SI 2 + 2P + 8H-O = 2K-HP0 1 + 14HI. 



Hydriodic acid greatly resembles hydrochloric acid ; it is colourless, and highly acid, 

 it fumes in the air, and is very soluble in water. Its density is 4 '4, and under strong 

 pressure it condenses to a yellowish liquid, which solidifies at 60 Fahr. 



Hydriodic acid in solution is much more easily prepared by suspending iodine in 

 water, and passing a stream of washed hydrosulphuric acid through it until the 

 colour disappears ; it is then heated to expel the hydrosulphuric acid, then allowed to 

 rest, when it may be decanted from the precipitate of sulphur. The reaction consists 

 simply in the displacement of the sulphur by the iodine, HS + 1 = HI + S. 



This liquid may be evaporated until it acquires a density of 1*7, when it consists of 

 HI+11HO. It then distils at 262 Fahr. without decomposition. The solution 

 cannot be long kept, it being decomposed by the oxygen of the air with the liberation 

 of iodine, which imparts a dark colour to it. Chlorine decomposes it instantly, with 

 liberation of the iodine. 



The solution of hydriodic acid and of the iodides possess the power of dissolving a 

 considerable quantity of iodine, forming a dark solution. H.K.B. 



HYDROBENZOIRT. A compound produced by the action of nascent hydrogen 

 on benzoyl hydride bitter almond oil. See BENZOLE. 



HYDROBROIVTIC ACID. See BROMINE. 



HYDRO-CARBON'S. Compounds consisting of carbon and hydrogen only. See 

 CAHBURETTED HYDROGEN : see also Watts's ' Dictionary of Chemistry.' 



HYDROCHLORIC ACID, Chlorhydric acid, or hydrogen chloride. (Acide 

 chlorhydrique, Fr. ; Salzsdure, Ger.) Sym. HC1. ; at. weight, 36 - 5. A compound of 

 chlorine and hydrogen, which is a colourless gas, of a peculiar suffocating, pungent 

 odour ; it reddens vegetable blues, but possesses no bleaching properties. The solution 

 of hydrochloric acid in water is the muriatic acid and spirit of salt of commerce ; 

 anciently marine acid. 



Hydrochloric acid gas may be obtained by the direct union of its elements hydrogen 

 and chlorine. By exposure to sunlight, by passage of an electric spark, or by direct 

 contact with flame, these two gases unite with explosive violence. 2 volumes of 

 chlorine and 2 volumes of hydrogen combine to form 4 volumes of this acid. Its 

 specific gravity is 1'247, air=l'000. 



By sealing up muriate of ammonia and sulphuric acid, apart, in a strong glass tube 

 re-curved, and then causing them to act on each other, Sir H. Davy procured liquid 

 muriatic acid. At 50 F. it condenses under a pressure of 40 atmospheres, to a liquid 

 of spec. grav. 1-27. 



Hydrochloric acid is best prepared by heating a mixture of 6 parts of chloride of 

 sodium (common salt) and 10 parts of concentrated sulphuric acid previously diluted 

 with 4 parts of water, in a capacious glass retort, connected with a set of Woolfe's 

 bottles. This acid is extracted on a large scale from sea-salt, by the action of sulphuric 

 acid at a moderate heat ; but it was originally obtained from the salt by exposing a 

 mixture of it and of common clay to ignition in an earthen retort. The acid gas which 

 exhales is rapidly condensed by water. 100 cubic inches of water are capable of ab- 

 sorbing no less than 48,000 cubic inches of the acid gas, whereby the liquid acquires 

 a specific gravity of 1*2109, and a volume of 142 cubic inches. This vast condensa- 

 tion of the gas is accompanied with a great production of heat ; whence it becomes 

 necessary to apply artificial refrigeration, especially if so strong an acid as the above 

 is to be prepared. In general, the muriatic acid of commerce has a specific gravity 

 varying from M5 to 1'20, and contains, for the most part, considerably less than 40 

 parts by weight of acid gas in the hundred. The above stronger acid contains 42'68 

 per cent, by weight ; for since a cubic inch of water, which weighs 252'5 grains, has 

 absorbed 480 cubic inches = 188 grains of gas ; and 252'5 + 188 = 440'5 ; then 440*5 : 

 188:: 100 : 42-68. In general a very good approximation may be found to the per- 

 centage of real muriatic acid, in any liquid sample, by multiplying the decimal figures* 



