368 The Philosophical Society of Glasgow. 



elevated temperature for a lengthened period of time. In the first 

 experiment a quantity of the syrup was heated in a sand bath until a 

 large proportion of the sugar crystallized out ; more water was then 

 added, and the evaporation and solution repeated two or three times. 

 A thick syrup was thus obtained, which refused to give any crystals 

 when kept for weeks over oil of vitriol. Analysis gave fourteen parts 

 of fruit to one of cane sugar. In the next experiment the syrup was 

 kept in the bastard loft of a sugar-house (temperature 90° to 100°) 

 for several months, water being added from time to time. A thick, 

 almost semi-solid, syrup was thus obtained, which did not show the 

 slightest appearance of crystals even under the microscope. At this 

 time it contained only one part of cane to ten of fruit sugar. The syrup 

 was left exposed in the same vessel for some time afterwards without 

 undergoing any apparent change, when suddenly the whole was trans- 

 formed into a soft solid mass, consisting of distinct but microscopic 

 crystals of grape sugar. Weak acids give rise to the formation of grape 

 sugar ; but this change does not appear to begin until all the cane 

 sugar has first been converted into fructose. I have never observed 

 crystals of grape sugar in any of the ordinary products of the sugar- 

 house, even in the strongest and heaviest syrups. It is true that 

 minute crystals generally appear in heavy syrups and molasses, when 

 kept for some time, but these are seen, on examination by a low power 

 of the microscope, to consist of cane sugar crystallized in the usual 

 form. Fruit sugar does not crystallize at all, but forms, on evapora- 

 tion, a tenacious semi-solid mass. Grape sugar crystallizes readily 

 enough, from a tolerably strong solution which has not been exposed to 

 too high a temperature. 



With regard to the natural distribution of tlie two varieties of sugar, 

 it appears tliat all sweet vegetable juices, which are alkaline or neutral, 

 contain cane sugar only; while those that are acid, contain fruit sugar 

 onlv. The two sugars have never been found mixed together in the 

 juices of plants. It is unfortunately but too easy to change cane sugar 

 into fruit or grape sugar, but the reverse process cannot be effected by 

 artificial means. 



Cane sugar crystallizes readily in fom'-sided prisms with rhomboidal 

 base, but the crystals have generally a cubical appearance ; and some- 

 times, by truncation, they assume the aspect of six-sided prisms. The 

 crystals are always sharp in the edges and solid angles, even when pro- 

 duced from the most impure syrups, Cane sugar is distinguished from all 

 other bodies by its intensely sweet taste, which is best observed when 

 the sugar is in fine crystals, as the sensation of sweetness depends very 

 much upon the rapidity of solution. Wc frequently hear one kind of 



