100 BULLETIN OF THE BUSSEY INSTITUTION. 
seen to be beset with the blunt spines which are characteristic of 
this substance; on recrystalling the bails from diluted alcohol 
(3 parts alcohol of 95% and 1 part water) clear cut crystals and 
plates of mannose hydrazone were obtained. 
It is worthy of remark that less favorable results were obtained 
in experiments where potassium dichromate was used instead of the 
hydrogen dioxide to oxidize mannite. It was made evident that 
the dichromate is less convenient than the dioxide for this purpose, 
though it might be made to serve fairly well in case the dioxide 
was not to be had. For example, a solution containing 0.2 grm. 
of mannite was treated with 1 cc. of dilute sulphuric acid and 
20 drops of a 1:25 solution of potassium dichromate and the mix- 
ture was boiled for 1 minute. When cold it was nearly, but not 
quite, neutralized with sodium hydroxide, and sulphuretted hydro- 
gen was passed to saturation to reduce the excess of chromic acid. 
The liquid was made faintly alkaline, filtered, acidulated slightly 
with sulphuric acid, and evaporated to soft dryness. The residue 
was taken up with 1 ¢.c. of water, the solution was filtered, and 
16 drops of the phenylhydrazin acetate solution were added to it. 
Next day balls of mannose hydrazone, as well as osazone crystals, 
were plainly visible. Similar results were obtained in another 
trial where no sulphuretted hydrogen was applied to reduce the 
excess of chromic acid. 
Precipitation of Mannite by means of Ammoniacal Copper 
Sulphate. 
Experiments were made also to test the question whether the 
method of precipitating mannite with ammoniacal copper sulphate, 
as proposed by Guignet,* is delicate enough for the purposes of 
the present enquiry. As will be seen below, this method has con- 
siderable merit, though a better method is still to be desired. 
To prepare the ammoniacal compound, crystallized copper sul- 
phate in fine powder that has been dried for several hours at: 
100° C. is added little by little to strong ammonia. As soon as a 
deep blue precipitate begins to separate from the dark blue liquor 
the whole is boiled for a few minutes and is then allowed to cool. 
Fine blue needles separate, from which the mother liquor is re- 
* Comptes Rendus, 1889, 109. 528. 
