430 PRINCIPLES OF CHEMISTRY 



solution. Common salt is somewhat soluble in alcohol, 21 but it is 

 insoluble in ether and in oils. 



Common salt gives very few compounds 2a (double salts) and these 

 are very readily decomposed : it is also decomposed with great difficulty 

 and its dissociation is unknown. 23 But it is easily decomposed, both 

 when fused and in solution, by the action of a galvanic current. If the 

 dry salt be fused in a crucible and an electric current be passed through 

 it by immersing carbon or platinum electrodes in it (the positive elec- 

 trode is made of carbon and the negative of platinum or mercury), it is 

 decomposed : the suffocating gas, chlorine, is liberated at the positive 

 pole arid metallic sodium at the negative pole. Both of them act on tho 

 excess of water at the moment of their evolution ; the sodium evolves 

 hydrogen arid forms caustic soda, and the chlorine evolves oxygen and 

 forms hydrochloric acid, and therefore on passing a current through a 

 solution of common salt metallic sodium will not be obtained but 

 oxygen, chlorine, and hydrochloric acid will appear at the positive 

 pole, and hydrogen and caustic soda at the negative pole. 23 Hs Thus 

 salt, like other salts, is decomposed by the action of an electric current 

 into a metal and a haloid (Chapter III.) Naturally, like all other 

 salts, it may be formed from the corresponding base and acid with 

 the separation of water. In fact if we mix caustic soda (base) 

 with hydrochloric acid (acid), table salt is formed, NaHO + HC1 

 = NaCl + H 2 0. 



21 According to Schiff 100 grams of alcohol, containing jp p.c. by weight of C 2 H ti O, 

 dissolves at 15 



p = 10 20 40 60 80 



28-5 22-6 13-2 5'9 1'2 grams NaCl. 



22 Amongst the double salts formed by sodium chloride that obtained by Ditte (1870) 

 by the evaporation of the solution remaining after heating sodium iodate with hydro- 

 chloric acid until chlorine ceases to be liberated, is a remarkable one. Its composition is 

 NaI0 3 ,NaCl,14H 2 0. Rammelsberg obtained a similar (perhaps, the same) salt in well- 

 formed crystals by the direct reaction of both salts. 



23 But it gives sodium in the flame of a Bunsen's burner (see Spectrum Analysis), 

 doubtless under the reducing action of the elements carbon and hydrogen. In the 

 presence of an excess of hydrochloric acid in the flame (when the sodium would form 

 sodium chloride), no sodium is formed in the flame and the salt does not communicate 



i its usual coloratiqn. 



23 bis There is no doubt, however, but that chloride of sodium is also decomposed in 

 its aqueous solutions with the separation of sodium, and that it does #ot simply enter 

 into double decomposition with the "water (NaCl + H 2 O = NaHO + HC1). Thla is seen 

 from the fact that when a saturated solution of NaCl is rapidly decomposed by an electric 

 current, a large amount of chlorine appears at the anodo and a sodium amalgam forme 

 at the mercury cathode, which acts but slowly upon the strong solution of salt. 

 Castner's process for the electrolysis of brine into chlorne and caustic aoda is an 

 application of this method which has been already worked in England, on aji industrial 

 cale. 



