132 Intelligence and Miscellaneous Articles* 



carbonate of soda, and of anhydrous sulphate of soda; the first from 

 the 3()th of October to the -l-th of December, and the two last from 

 the 31st of October to the 4 th of December. The crystals of sul- 

 phate of soda began in one day to effloresce, and on the 9th of De- 

 cember they had lost 9| grains; and Mr. Watson concludes that if 

 the exposure had been continued they would have become anhy- 

 drous. The anhydrous sulphate gained no weight. On the 1st of 

 November, the crystals of carbonate of soda were found neither to 

 have lost weight nor to have effloresced in the slightest degree ; on 

 the 5th, some of the outside crystals were slightly effloresced, which 

 appeared to be in consequence of the lowness of the vapour point 

 on the 2nd (11° below the temperature), and also on the 4th (lO'* 

 below the temperature); on the 11th, these crystals were no more 

 effloresced than they were on the 5th ; by the 10th December, how, 

 ever, efflorescence was considerably more apparent, though even 

 then it had not made a great advance ; in the interval between the 

 11th of November and the ^th of December, the vapour point had 

 several times been 10° and IP below the temperature, which was 

 undoubtedly the cause of this further efflorescence. 



The conclusion drawn by Mr. Watson from the above and other 

 similar experiments is, that the crystals of carbonate of soda begin 

 to effloresce at the temperature of 58°, when the vapour point is at 

 48°, and that the crystals of sulphate of soda begin to effloresce at 

 the temperature of 58°, when the vapour point is at 49°; and there- 

 fore, that the carbonate may be left exposed to the atmosphere at 

 the temperature of 58° when the vapour point is not lower than 49°, 

 and the sulphate when the vapour point is not lower than 50*', with- 

 out any of their water of crystallization being lost ; and since the 

 atmosphere in those states of dryness is capable of evaporating un- 

 combined water, we have beautiful means afforded of providing 

 ourselves with the salts in question free from any water not belong- 

 ing to the constitution of the crystals, but at the same time, with 

 all that does belong to it. As the crystals of sulphate of soda only 

 begin to effloresce at the temperature of 58° when the vapour point 

 is 49°, Mr. Watson considers that when the vapour point is only at 

 50° then the affinity of space for vapour is just equal to the affinity 

 of this salt for its water of crystallization. The ordinary phosphate of 

 soda appears to possess the same efflorescing property as the 

 carbonate. — 



DETECTION OF COMMON SALT IN CHLORIDE OF POTASSIUM. 



Mr. Watson in the paper from which the above extract is made, ob- 

 serves that it is sometimes a desideratum to ascertain if and to what 

 amount muriate of potash [chloride of potassium] (an article much 

 used in the manufacture of alum) is adulterated with common salt. 

 The means, he observes, which would hitherto be used to accomplish 

 that object are tedious. Jf, however, a solution of a sample of the 

 kind in question be treated with sulphate of ammonia till all the 

 chloride is converted into sulphate, and the resulting mixture be 

 evaporated to dryness, and calcined till all the ammoniacal salt is 

 dissipated, the residue will be the anhydrous sulphate of the alkali 

 or alkalis of the sample; by placing this under an exhausted re- 



