[ 202 J 

 XLIl. On Magnesia- Sul(j/iale of Soda. By Mr. J. Healej. 



. To Mr. rUloch. 



Sir, — A coMMUNK ATioN, I ohserve, has been presented to 

 the Royal Society of Edinbmgh, by Dr. Murray, on the analysis 

 of sea water, the first part of which was read April the 15th, 

 and the conchision on the 20th of May last. It is there shown 

 by this excellent chemist, that the brine or mother-lirjnor of 

 sea-water abounds with a salt, which, he says, "seems hitherto 

 to have escaped observation. It is a compound of the sulphates 

 of magnesia aiid of soda, which together crystallize in very re- 

 gular rhombs, occasionally truncated on some of the edges and 

 angles ; and this compound salt contains a nmch smaller i|uan- 

 tity of water of crystallization than either of the sulphates of 

 which it is formed; is less disagreeable to the tastre ; differs 

 from both in all its other properties; and has not hitherto been 

 applied to any useful purpose, but may probably form a very ex- 

 cellent purgative salt*." 



Tins aperient salt has certainly been long in use, althoxigh 

 we fmd no exact account of its qualities or any description of its 

 composition published. It was sold, I am informed, many years 

 ago under the name of Lyminglon Glauber's salt ; it was then 

 considered as an adulleration, and therefore brought an inferior 

 price in the market. At that time, the true Glauber's salt was 

 very costly, and chiefly obtained in the process for muriatic 

 acid ; but the improved methods of preparing the crude muriate 

 of ammonia have greatly reduced the value, so much so that the 

 Lvmington salt is no longet sold as a snlstitute for Glauber's, or 

 the sulphate of soda. 



Vv'hether the extensive works at Lymington furnished this salt 

 simply by evaporating the brines, or by mixing the two sulphates 

 in some certain proportions, I cannot determine ; I have, however, 

 seer, an (>ld prescription for preparing it, which consists in mixing 

 two parts of sulphate of soda with one of tlie sulphate of magne- 

 sia, and in the usual way procppding to crystallize the product. 



That this compound salt, which for the present may be called the 

 vingncsin-siilpkuie of soda, is the chief ingredient in many f)f the 

 natural saline aperient springs, and gives tlie pingative quality to 

 sea-water, 1 have scarcely anv doul)t; and when its coiriposition 

 shall have been more attentively examined, vve shall probably 

 find that in every case it will consist of difinilc proportions of 

 its three components, — sulphuric acid and tiie two bases, viz. 

 soda and magr.csia. 



The analysis of a mineral water, as Dr. Saunders justly ob- 

 serves, had better be incomplete than inaccurate ; and Dr. 

 Fothcrgill's experimental inquiry concerning the Cheltenham 



* New Journal of the Royal Iiibtitution of Great Britaiu, vol. i. p. 294. 



