870 Dr. Prout on the ultimate composition 
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 fre- 
quent 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 
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 pur- 
poses of experiment.f At length my stock became 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. 
f See Annals of Philosophy, iv. 424 (N. S.) I do not distinctly remember 
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 experiments on the sugar of 
commerce. 
