of simple alimentary Substances, fyc. 99 



As a subject of general interest to chemists, as well as of 

 considerable importance in the present inquiry, I shall also 

 attempt to investigate the composition of a few of the com- 

 pounds of the saccharine principle with oxygen, or what are 

 usually denominated the vegetable acids. 



Of Sugars. 



Many analyses of sugar have been published by different 

 chemists, no two of which agree with each other. These dis- 

 crepances have doubtless arisen from various causes, though 

 one cause has probably been some real or accidental difference 

 in the composition of the sugars employed*. How many 

 distinct varieties of sugar exist I do not pretend to know, but 

 there are at least two, (independently of the sugar of milk, 

 manna, &c. which belong to another series,) and probably 

 there are several others ; and it is to the mixture or combination 

 of these in different proportions, and the frequent presence of 

 foreign bodies, that a good deal of the confusion respecting 

 the composition of sugar has undoubtedly risen. 



Cane Sugar. — The strongest and most perfect sugar that I 

 am acquainted with, is sugar candy carefully prepared from 

 cane sugar. This, purified by repeated crystallizations from 

 water and alcohol, and deprived of the little hygrometric 



* Some years ago I published an analysis of sugar, in which the propor- 

 tions of carbon to water were stated to be to one another as 40 : 60. I was 

 not aware at that time of the differences existing among sugars, and the 

 results given were founded on the analysis of a specimen of remarkably fine 

 looking sugar candy, a quantity of which I had purchased and kept by me 

 for several years for the purposes of experiment 8 . At length my stock be- 

 came exhausted, and I was surprised to find on analysing other specimens, 

 that they in general contained upwards of one per cent, more of carbon 

 than what I had before examined. This induced me to recur to the notes 

 of my former experiments, but I could detect no material error in them ; 

 and though I readily admit that the apparatus I then employed was much 

 less susceptible of accuracy than what I now use, I cannot help thinking 

 that the candy itself was partly in fault, and that it was prepared from an 

 imperfect sugar, probably from the East Indies. 



There was also another circumstance which contributed to mislead me, 

 not only in this but in all my other results, viz. an inaccuracy in the weight 

 usually assigned to atmospheric air, at least as regarded my weights. I have 

 long suspected the perfect accuracy of this datum as settled fifty years ago by 

 Sir G. Shuckburgh, and have been accustomed for some time past to make 

 an allowance for it ; but I was not aware till recently of its exact amount, 

 when I was induced to undertake a series of experiments on the subject, 

 which I hope shortly to lay before the public. 



a See Annals of Philosophy, iv. 424 (N. S.) I do not distinctly remem- 

 ber whether, at the time this paper was published, some of the original 

 sugar candy existed or not, but I had then only made one or two experi- 

 ments on the sugar of commerce. 



O 2 moisture 



