Professor Johnston on the Sugar of the Eucalyptus. 15 



the same constitution as grape-sugar, C 12 H14 14 , or C 24 

 H 28 28 , but it differs from grape-sugar in its appearance, 

 in its relations to alcohol as above described, in the ease with 

 which it can be obtained in a pure crystallized form, and in 

 its relations to heat. 



When suddenly heated at once to 200° or 212°, it melts 

 and loses 5 atoms of water, whereas grape-sugar loses only 

 four. But if it be first gradually heated and kept for two or 

 three hours at 180° only, it will part with seven atoms of 

 water without melting. In that respect it resembles a salt, 

 which if heated suddenly will melt in its water of crystalliza- 

 tion, but by a cautious regulation of the heat may be dried 

 without undergoing fusion. If once melted, this sugar may 

 be kept for several hours at 212° without losing much more 

 than the five atoms, and it must be raised to 240° or 250° 

 before it parts with the whole seven, and in every case in 

 which I have made the experiment has even assumed a brown 

 colour, owing to incipient decomposition before the seven 

 atoms have been altogether removed. 



When die seven atoms have been driven off by a heat not 

 higher than 200°, the dry powder may be heated to 280°, 

 when it begins to fuse, and may be kept for several hours at 

 300° without further loss or any change of colour. 



After being thus heated the sugar attracts moisture rapidly 

 from the air, and if left over night in a damp room it will 

 assume the form of transparent globules of syrup, which gra- 

 dually crystallize into colourless radiated masses having the 

 original weight of the portion of sugar experimented upon. 

 We may conclude therefore that the seven atoms are alto- 

 gether water of crystallization. 



When mixed with oxide of lead moistened with water and 

 then gradually dried and heated to 300°, it appeared to lose 

 two additional atoms of water without undergoing decom- 

 position ; but when exposed to the air on cooling, the mix- 

 ture rapidly attracts water again from the air. When this 

 mixture after thus heating is boiled with distilled water and 

 thrown upon the filter, a solution of sugar passes through in 

 which hydrosulphurets detect no trace of lead. 



The following formulae exhibit the constitution of this sugar 

 and the loss of weight it undergoes at different temperatures : — 



Loss by experi- 

 Crystallized sugar before! n „ merit, per cent. 



or after heating . . .J U *4 "21 ^21 + 7 HU 

 Fused at 212° to 220° . C 24 H 21 21 + 2 HO 11-23 

 Dried without fusion be-~l r H n 



tween 180° and 300° J ^ 24 " 21 Uai 15 ' 88 



