of Plate-sulphate of Potash. 405 



These proportions correspond to the formula 3K0 SO^, NaO 

 SO^, as shown in the third column of the above statement. 



The presence of soda in the salt was easily established by 

 decomposing a known quantity with nitrate of baryta, and cry- 

 stallizing the solution filtered from the precipitate. Crystals of 

 nitrate of soda mixed with those of nitre were abundantly depo- 

 sited. In another experiment, a known quantity of the salt dis- 

 solved in water was decomposed by chloride of barium, and the 

 solution, separated from the precipitate by filtering, was evapo- 

 rated to dryness ; and the mixed chlorides, after treatment with 

 bichloride of platinum, were tested with the delicate and beautiful 

 process for the detection of soda proposed by Dr. Andrews at 

 the Meeting of the British Association in Belfast*. 



It will be at once remarked, that the composition of this salt 

 does not correspond to that of any other double salt of potash. 

 The atomic proportions of its ingredients are at variance with 

 our ordinary notions of the constitution of these compounds. I 

 hope, however, to be able to explain the anomaly by the exami- 

 nation of other compounds of sulphate of potash, and of chro- 

 mate of potash, which I have in process of preparation. 



In Gmelin's ' Chemistry t/ it is incidentally mentioned that 1 

 part by weight of dry carbonate of soda, and 2 parts of bichro- 

 mate of potash, give crystals having the same form as sulphate 

 of potash, and containing 3K0 CrO^, NaO CrO^, which cor- 

 responds exactly with plate-sulphate of potash. It is also stated 

 that crystals containing about 2K0 SO'', NaO SO^, may be 

 prepared by fusing equal atomic proportions of the two sul- 

 phates, and crystallizing the mixture from water. Rose made 

 sevei'al analyses of the salt, obtained by crystallizing together 

 the sulphates of potash and soda ; but the discrepancies in the 

 results led him to doubt the definite composition of the crystals. 

 Dr. Gladstone! has made a series of experiments with a view 

 to produce a definite double sulphate of potash and soda. He 

 crystalhzed various mixtures of the two sulphates, and obtained 

 a salt to which he ascribed the formula 5K0 SO^, NaO SO^. 

 Such a compound would contain 46"44 per cent, of potash, and 

 47'43 of sulphuric acid. 



In several of its physical characters, the plate-salt differs essen- 

 tially from neu'ral sul])hate of potash. It is, for example, more 

 readily fusible, and it may be melted without much difficulty in 

 a platina crucible with the ordinary gas-blowpipe; whereas sul- 

 phate of potash is only slightly softened at the edges, even when 

 the blast from the bellows is urged to the fullest extent; it 

 requires the full bright red heat of a furnace for perfect fusion. 



* Chemical Gazette, vol. x. t Vol. i. p. 108. 



X Quarterly Journal, vol. vi. 



