96 ^n Analysis of Sea-water ; 



The difficulties attending the perfect separation of com- 

 pound salts from each other, by crystallization, even with the aid 



the intermixture of muriate of soda and muriate of magnesia, and perhaps, 

 also, of sulphate of soda, is dissolved in M'ater, and by evaporation and cool- 

 my; is obtained crystallized ; a fresh quantity of it is added to the residual 

 liquor, and by the necessary evaporation and cooling, a new crvstallizatioti is 

 produced ; this is repeated for a third or fourth time ; and it is in tliese latter 

 crystallizations that this triple salt is formed, frequeirtly in considerable quan- 

 tity, and usually at a high temperature, being precipitated even in the boiler. 

 It crystallizes in rhombs, at first irregnlar and semitransj)arerit; but by so- 

 lution in water, and a second crystallization, is obtained in more regular 

 rhombs, truncated on the acute angles, on the obtuse angles and edges, an<! 

 on the terminal edges, considering the rhomb as a four-sided prism, and trans- 

 parent. The crystals are permanent in the air ; they are soluble in little more 

 than three times their weight of water, at the temperature of GO" ; they do 

 not undergo the watery fusion from heat, but suffer decrepitation. In these 

 properties, this salt differs entirely from sulphate of soda, or sulphate of 

 magnesia. ^ 



To detemiine its composition, 20 grains reduced to powder were expose<l 

 to heat, raised gradually nearly to redness ; they lost from the escape of water 

 5-6 grains. The residual powder was dissolved in water, and muriate of ba- 

 rytes was added as long as any precipitation was produced. The precipitate 

 dried at a red-heat, weighed 23-\) grains, equivalent to sulphuric acid 8-2 

 grains. To the clear liquor carbonate of ammonia was added, which did not 

 impair the transparency; phosphoric ticid was then dropped in, which pro- 

 duced a copious precipitation. The precipitate, calcined at a red-heat» 

 weighed 5-3 grains, equivalent to 2-1 of magnesia, or 6'4 of sulphate of 

 magnesia ; the residual liquor being evaporated to diyness, the dry mass was 

 submitted to heat, gradually raised, as long as any vapours exhaled ; it af- 

 forded, by solution in water and evaporation, muriate of soda in cubes, which, 

 after exposure to a red-heat, weighed 6'4 grains, equivalent to 7'^ grains 

 of sulphate of soda. 100 grains of the salt, therefore, afford of 



Sulphate of magnesia, - - - 32 grains. 



soda, - - - - ."W 



Water of crystallization, - - 28 



Loss, -...-■-_- 1 



loo 



It afforded also a slight trace of muriatic acid ; its solution being in a very 

 slight degree rendered turbid by nitrate of silver, probjibly owing to the in- 

 termixture of a little muriate of soda, as an extraneous ingredient. This 

 accounts for the proportion of sulphuric acid, as inferred from the quantities 

 of the bases, being a little larger than that directly obtained by the precipi- 

 tation by muriate of barytes. 



The difference of crystalline form, as well as other differences of properties, 

 in the salt, from those either of sulphate of soda or sulphate of magnesia, 

 sufficiently prove that it is not merely an intermixture of the two, but that it 

 is of definite composition. It deserves to be remarked, too, that it has not 

 the same lelation to water that either of these salts has, o« any meai* 

 between them; the quantity of its water of crystallization being consider- 

 ably less. Its taste is much less disagreeable than that of sulphate of soda, 

 or sulphate of magnesia ; it might therefore probably be introduced with 

 advantage as a purgative salt, especially as it could be procured at a low 

 price ; and from its composition, it would afford a very good substitute for 

 the aperient mineral waters, which usually owe their activity to sulphate of 

 soda and sulphnte of magnesia. 



of 



