IJQ EFFLORESCENCES OF WALlS. 



precipitate, while the latter had no perceptible operation j a 

 decifive teft of the exiftence of magnefia, which was fug- 

 gefted to me by Mr. William Henry of Manchefter. This 

 fait appeared, therefore, to be a very pure fulphate of mag- 

 nefia. 

 The fccond cf- The fecond efflorefcence which I examined was obtained 

 X'S"of foda ^'"O"^ ^^^e outer wall of a ftable, winch had been ereded for 

 with indication fome ycais. It differed on its appearance from the two 

 ofmuriaticadd.^^j.^jgj.. inftead of (hooting out from the wall in fpiculae of 

 confiderable length, it appeared like a powder fcattered over 

 the furface, occupying diflind, round patches, fo as in fome 

 degree to refemble the growth of a grey lichen. The bricks 

 on which this efflorefcence appeared were in general of a 

 * fofter texture than thofe of the reft of the wall. Though it 



occupied a confiderable extent, it was difficult to colled it in 

 any quantity, but I obtained fufficient to fubjedl it to the fol- 

 lowing experiments. The fait was diffblved in warm water, 

 filtered and cryflallized ; the cryftals were very foluble at the 

 common temperature of the atmofphere. Muriate of Barytes 

 added to the folution produced a copious precipitate ; car- 

 bonate of pot-afli, pure pot-afli, pure ammoniac and oxalic 

 acid were refpedively added to the folution, but produced no 

 effed. Nitrate of filver caufed a precipitate, but only in 

 fmall quantity. From thefe experiments it appeared that the 

 fait in queftion confifted of the fulphuric acid, mixed with a 

 fmall proportion of the muriatic, and combined with one of 

 the fixed alcalies. From the form of its cryftals I conceived 

 that the fulphuric acid was in this cafe united to foda, but the 

 quantity of fait which had been procured, was not fufficient 

 to enable me to determine accurately from this circum- 

 ftance. A more decifive teft between the fulphate of foda 

 and the fulphate of pot-afli, is the property which the latter 

 alone poflefles of forming alum with the acid fulphate of 

 alumine. I accordingly prepared a quantity of this fubftance ; 

 to one portion of it fulphate of pot-a(h was added, and to the 

 ©ther fome of the fait under examination. By gentle evapo- 

 ration and fubfequent cooling, the firft produced very evident 

 cryftals of alum, the latter only formed a confufed mafs. This 

 1 confidered as a fufl^icient proof that this faline efflorefcence 

 was the fulphate of Ibda. 

 Thirii cfflorcf- ^he third efflorelcence was obtained from the inner walls of 

 cencc fulphate a brick houfc which was then erecting ; it had all the internal 



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