1813.] Scientific Intelligence, . . 381 



fluici, even if taken up with care, and solidification does not ensue 

 until agitation takes place. 1 bad made a solution of this salt 

 in a large vial to the full extent that the wdter could take up by 

 exposure to an almost naked fire. At this time I vi^as obliged to 

 leave it, and neglected to cork it, fully expecting the next day 

 to find it completely solid. It was, however, perfectly fluid ; 

 but solidified almost instantly on my taking it from the table. 

 Since that period I have annually exhibited to my Class bottles 

 equally strong in solution, some corked, and others uncorked, 

 and both remaining fluid at the end of 24 hours, and becoming 

 solid by the usual means of agitation after the cover of the 

 former \vas penetrated, and by shaking the latter. I have also 

 found occasionally bottles thus prepared and corked, solidified 

 where I had no reason to expect it ; and frequently 1 have seen 

 a part of the salt reduced to a solid form in a close bottle, and 

 when opened and shaken the whole becoming solid, with a sin- 

 gular change in the appearance of that part of the salt which 

 had been previously precipitated. It assumed, whilst the latter 

 precipitation or formation of crystals was going on3 a very beau- 

 tiful porcellanous white appearance, which remained permanent 

 at the bottom of the last formed crystalline mass, and i have 

 now some in that state thus produced during the last winter. It 

 has occurred so frequently, that I cannot consider it accidental; 

 but I am at a loss to explain the fact. From mere appearance I 

 should conclude the salt thus previously produced had entirely 

 given up its water of crystallization c That something more than 

 mere atmospheric pressure is necessary, however, to explain the 

 common occurrence cannot, I think, be denied. I shall be glad 

 to find it succeed in your hands, and to have your opinion 

 respecting it. If the common explanation was correct, why 

 can we not eftect the same with nitrate of potash ? I have 

 rpeatedly tried, but ineffectually. 



I have several times, since I Vv^rote to you last, tried the 

 reforming of pyrophorus, by adding a portion of solution of 

 potash to imperfect pyrophorus, and exposing to heat, with 

 complete success. I have, therefore, little doubt of the whole 

 phenomena being dependant on the formation of a portion of 

 potassium spread through the mass, and inflaming through the 

 instrumentality of atmospheric moisture, &c. I have even once 

 tried it successfully on pyrophorus already ignited by exposure 

 to the air ; and hence it may be useful to preserve that which 

 has undergone the change, till a sufhcient quantity is obtained 

 to be again treated with the addition of potash, since it will 

 save the trouble of the preliminary steps, and we have at hand 

 the materials in a very dry and perfect state for the process. 



V. Use of Magnesia in Calculous Diseases, 

 TJie Editor is requested by Dr. Henjy to state, that he never 



