470 SODIUM. 



taining a smaller excess of carbonic acid. The theoretical 

 carbonate of water, supposed to resemble the carbonate of magne- 

 sia, will be HO, CO 2 , HO + 2HO; which gives the salt in ques- 

 tion, if the last 2 HO are replaced by two proportions of proto- 

 hydrated carbonate of soda. Substitutions of this character 

 appear to be common, in the formation of double carbonates and 

 oxalates. The bicarbonate of potash may be formed by the 

 substitution of carbonate of potash for the first HO, in this car- 

 bonate of water, while the other 2HO disappear. This salt oc- 

 curs native in several places, particularly on the banks of the 

 lakes of soda in the province of Sukena, in Africa, whence it is 

 exported tinder the name of Trona, in Egypt, Hungary, and in 

 Mexico, and has the same proportion of water as the artificial 

 salt. 



Sulphate of soda, Glauber's salt; NaO, SO 3 -f 10HO; 892.1. 

 -f 1125, or 71.48 + 90. This salt occurs crystallized in nature, 

 and also dissolved in mineral waters, and is formed on neu- 

 tralising carbonate of soda by sulphuric acid. But it is more 

 generally prepared by decomposing common salt with sulphuric 

 acid, as in the process for hydrochloric acid (page 3rt2.) The 

 sulphate of soda crystallizes readily in long prisms, of which the 

 sides are often channeled, which have a cooling and bitter taste, 

 and contain 55.76 per cent of water, or 1 equivalents ; in which 

 they fuse by a slight elevation of temperature, and which they 

 lose by efflorescence in dry air. At 32, 100 parts of water dis- 

 solve 5.02 parts of anhydrous sulphate of soda, 50.65 parts at 

 !)1, which is the temperature of maximum solubility of this 

 salt, and 42.65 parts at the boiling temperature. In a super- 

 saturated solution of this salt (page 263), crystals are sometimes 

 slowly deposited, which are different in form and harder than, 

 Glauber's salt; they contain 8 equivalents of water. A satu- 

 rated solution of sulphate of soda, kept at a temperature be- 

 tween 91^ and 104, affords octahedral crystals with a rhombic 

 base, which are anhydrous. They are isomorphous with the 

 hypermanganate of barytes.* Their density is 2.642. The an- 

 hydrous salt fuses at a bright red heat, without loss of acid. 

 Sulphate of soda was at one time the saline aperient in common 



* Dr. Clark considers this isomorphism not fortuitous, and founds on it an 

 interesting speculation respecting the constitution of soda. It leads him to 

 double the atomic weight of sodium, or to estimate it at 582, which he 

 represents by So, and to make soda a peroxide, "So" O 3 , which like 

 other peroxides wnites with as many proportions of acid as it contains of 



