J 10 EFFLORESCENCES OF WALLS. 



Inveftigation of I ^^lall Conclude this communication by detailing to yon th^ 



the origin of progicfs which I have made in inveftigating the origin of the 



magSa on "he fulp'^ate of magnefia, which appeared in Mr. Earle's houfe. 



bricks of Mr. Belorc proceeding farther, it will be proper to obferve that 



Earle's houfe. the efflorefccnce was here altogether confined to the bricks, 



the mortar which united them being entirely free from it, and 



that rain water only had been employed in tempering the clay. 



It remained therefore to examine with accuracy, whether any 



fait, foluble in water, exifted ready formed in the clay, and 



what were the component parts of the clay itfelf. To afcer- 



tain the firil of thefe points, 60 grains of the clay powdered 



and dried were well waflied with boiling water ; the water 



was filtered and evaporated, and the refiduum carefully col- 



The clay con- ]qQq(\ . \i did not weigh i of a grain. It was re-difiblved in 



tained a por- • , , . , • r- 



tion of mu- water ; it produced a copious precipitate with the muriate ot 



riate and fulphate barytes, and the nitrate of fiiver; a very faint cloud with 



oxalic acid and with pure pot-ath ; ammoniac produced no 



effeft. The ready formed falts appeared therefore to be the 



fulphate and muriate of a fixed alcali, with a minute portion of 



the muriate of lime, the whole however exifting in very (mall 



quantity. 



And a larger Xhe clay itfelf w^as next examined : it was found to confifl 



portion of mae- •■,,,• ri ^ , • ■ , r- , 



nefia. principally ot lilex and alumine in the proportion or about 



three to one; the quantity of lime was very fmall, though 

 its exiftence was detected by the oxalic acid; its colour 

 ^ItsVed that it contained iron, and I alfo found that about 

 hve parts in the 100 confifted of magnefia. From this exa- 

 mination it appeared that one of the component parts of the 

 faltexifts in the clay ; I attributed the formation of the ful- 

 phuric acid to the fulphur which is frequently met with in our 

 coals, and wiiich I conceived might unite with oxigen during 

 Experiment to (he burning of the bricks. I attempted to put this action to 

 lul^hiTrfrom'the^h'^^^^f of experiment, and accordingly I formed a parte of 

 coals had given pipeclay and calcined magnefia in the proportion of 95 to 

 theacid?Doubt-^^,g. thig ^^s placed in a crucible, furrounded. with fmall 

 coal mixed with a quantity of fulphur ; the crucible was then 

 kept for fome time in a flrong heat. I was not able to deted 

 the prefence of the fulphuric acid in the clay that was thus 

 baked, but fo many circuraftances might aftually take place 

 in the formation and burning of the bricks, which we have it 

 not in our power to imitate in the laboratory, that I do not 

 confider the hypothefis difproved by my want of fuccefs. 



In 



