TRANSACTIONS OF THE SECTIONS. 45 



Carbon, 12 atoms = 9* 

 Hydrogen, 11 .. = 1'375 

 Oxygen 11 .. =11- 



21-375 



but the analysis requires repetition on a larger scale before any definite 

 conclusion on this particular subject can be drawn. 



It appears from the facts stated in this paper that there are three 

 species of sugar distinguished from each other by the quantity of wa- 

 ter which they retain when heated to as high a temperature as they 

 can bear without decomposition ; viz. common sugar, which may be 

 deprived of one atom of water by combining with oxide of lead ; dia- 

 betic sugar, which may in like manner be deprived of three atoms of 

 water ; and starch sugar, which by analogy may be presumed to be 

 capable of losing four atoms : so that all the species would, under 

 these conditions, become isomeric with anhydi'ous common sugar. 



If tliese views have any solidity, it would appear that sugar, like 

 pliosphoric acid^ has in all cases the same constitution, and that the 

 three states of it depend upon the quantity of water and probably of 

 other bases with which it is disposed to combine. 



Common sugar combines with one atom of water, diabetic sugar 

 with three, and starch sugar with four. There is doubtless a fourth 

 variety of sugar, not yet discovered, capable of uniting with two atoms 

 of water. 



All the three species are capable of undergoing fermentation and of 

 being resolved into 4 atoms carbonic acid and two atoms alcohol. 



4 atoms carbonic acid .... C^ O^ 



2 atoms alcohol C* H'^ O* 



C12 Hi2 O''^ 



Starch sugar has an excess of 2 atoms of water and diabetes sugar 

 of 1 atom ; while common sugar requires an atom of water to undergo 

 the decomposition. 



Dr. Thomson had previously mentioned that 39 65 grains of diabetes 

 sugar dried in vacuo over sulphuric acid, when exposed for 24 hours 

 to the heat of a steam-bath, lost 3*35 grains of moisture, and were of 

 course reduced to 36*3 grains. 



But 36-3 : 3-35 : : 23-625 : 2-18. 



It follows from this, that diabetes sugar dried over sulphuric acid is 

 deprived of two atoms of water when exposed to the heat of a steam- 

 bath or to 212°. The diabetes sugar, therefore, when in crystals, is 

 composed of 



12 atoms carbon ■=. 9* 

 15 atoms hydrogen = 1-8Y5 

 15 atoms oxygen = 15- 



25-875 



