iSi Dr. G. O. Rees on Hydrate of Magnesia. 



and the high lights sallow ; and where the delicately transpa* 

 rent tints shed their deepening beauty opacity gradually su- 

 pervenes. But those which are fixed in enamel will carry on 

 unchanged to a period indefinitely remote the most delicate 

 as well as the richest of the tints originally imparted by the 

 pencil of the artist; and as he left the portrait of the sage, the 

 poet, the warrior, and the beauty, so will they remain, when 

 even the marble which portrayed their forms or told their 

 history may have crumbled into dust. 

 35, Northampton-street, Clerkenwell, March 1837. 



LXXXVI. On Hydrate of Magnesia, By G. O. Rees, 

 M.D., KG.S., Src. 



To Richard Phillips, Esq., F.R.S., Sfc, 

 Dear Sir, 



SHOULD you think the following worthy of notice, pray 

 favour me by inserting it in the Philosophical Magazine. 

 Your sincerely obliged, 

 59, Guilford Street, Russell Square, G. O. Rees. 



May 16, 1837 



It has been supposed by some chemists that magnesia is 

 capable of uniting with water in several proportions, though 

 no analysis seems to have been made of the artificial hydrate 

 of that earth. The native hydrate of magnesia from America, 

 analysed by Dr. Bruce, yielded in 100 parts, 



Magnesia 70 



Water 30 100. 



A specimen of the same mineral from Unst, analysed by 

 Dr. Fyffe, yielded in 100 parts, 



Magnesia 69*75 



Water 30-25 100. 



The results of two analyses made by myself of the artificial 

 hydrate agree very nearly with the proportions obtained by 

 Dr. Fyffe from the native specimen. Thus in a first experi- 

 ment 100 parts yielded. 



Magnesia 69*63 



Water 30*37 100. 



A second experiment gave. 



Magnesia 6941 



Water 30*59 100. 



These specimens were prepared by digesting recently cal- 

 cined magnesia in cold distilled water and then drying the 



