4() EIGHTH REPORT — 1838. 



So that the atomic weiglit of tlie crystals of this sugar is 2.'j-875, and 

 it can be deprived of 5 atoms of water by combiniTig it Avilli oxide of 

 lead. 



Dr. Thomson then noticed & crystallized sugar obtamed from diabetic 

 urine by Mr. Macgregor of Glasgow, by Ambrosiane and Maitland 

 from the serum of blood in diabetes, and by himself in urine in a case 

 of diabetes, 1827. This sugar was in 4-sided prisms of 110° and 70* 

 white, translucent, sweetish, soluble in alcohol. This is believed by 

 Dr. Thomson to be a fourth kind of sugar, but having been interrupted 

 in his experiments upon it he recommends the subject to the attention 

 of chemists. 



On Galactin. By Thomas Thomson, M.D., F.R.S., Professor of 



Chemistry, Glasgow. 



This is a substance which constitutes the principal ingredient in the 

 sap of the Cow-tree, or Galaclodendron utile of South America, which 

 is used as a substitute for cream. The sap, on standing, throws up a 

 white matter, soluble in boiling alcohol, but deposited as that liquid 

 cools. When well washed and dried, in vacuo, over sulphuric acid, it 

 constitutes galactin. It is yellow, translucent, brittle, has a resinous 

 aspect, and is tasteless. It is insoluble in water, but becomes white 

 and soft by imbibing that liquid. It is soluble in alcohol and ether. 

 This white compound becomes soft and ductile at 60°; at 117° it is 

 still solid, but at 137° it is liquid. Abundance of aqueous vapour is 

 driven off, but the galactin does not become translucent and yellow till 

 kept some time at 170°. The specific gravity of pure galactin is 0-969. 

 It dissolves readily in oil of turpentine and olive oil. It does not com- 

 bine with potash, nor form a soap. Its con.^tituents are — 

 6 atoms carbon = 4*5, or per cent. 72 



6 hydrogen = 0'75 12 



1 oxygen = 1 16 



6-25 100 



being isomeric with Brazil wax, which does not, according to Mr. 

 Brande, form a soap with potash. 



Notice respecting the native Diarseniate of Lead. By Thomas Thom- 

 son, M.D., F.R.S., Professor of Chemistry, Glasgow. 



During the last meeting of the British Association at Liverpool, a 

 mineral dealer from Cumberland exposed a collection of North of 

 England minerals for sale. Among others there was one labeled vana- 

 diate of lead, from Caldbeck fell. On examining it. Dr. Thomson 

 thought that it differed too much, both in its colour and lustre, from 

 the true vanadiate of lead, of which he had been in possession for 

 some years, to be that mineral ; and, upon comparing it with the vana- 

 diate in his cabinet, this siispicion was confirmed. 



