426 
rorULAR SCIENCE REVIEW. 
of the serum of genuine milk diluted -with various quantities of water, we 
may obtain a standard of comparison which will enable us to say, within a 
few per cents., what quantity of water has been added to any sample of 
milk that may come under our notice. — Chemical News, August 5. 
A Simple Experiment in Reduction and Oxidation. — The following expe- 
riment has been described in the Berichte der Beutschen Chemischen Gesell- 
schaft zu Berlin, No. 12. — A well-polished small copper bell is placed in a 
ring on a triangle, and made red-hot by causing a strong gas flame to play 
upon it, so as to render the metal red-hot, and, consequently, very soon 
black. As soon as this is the case, a strong current of hydrogen gas is 
directed upon the metal, by means of a flexible tube fastened to the neck of 
a glass funnel large enough to cover the bell. As soon as the hydrogen 
comes into contact with the red-hot metal, the layer of black oxide of copper 
is removed, and the metal appears as before it was heated. By removing 
the current of hydrogen, the oxygen of the air again acts upon the hot 
metal j and thus this alternate oxidation and reduction may be continued, 
provided the metal had been made thoroughly red-hot to begin with. The 
hydrogen should be pure, and free from traces even, of sulphur or arsenic, 
in order that the experiment be successful. 
Reduction of Isatine to Indigo-Blue. — The Chemical News, in its admirable 
summary of the results of research abroad, gives the following note by 
Ilerren A. Bayer and A. Emmerling. They state that when isatine, pre- 
viously pulverised, is mixed with fifty times its weight of a mixture of equal 
parts of terchloride of phosphorus and chloride of acetyl, to which some 
phosphorus is added, and this mixture is heated for several hours to from 75° 
to 80° in a sealed tube, and the bright green coloured liquid contained in the 
tube poured into a large bulk of water, next filtered, and then left standing 
for twenty-four hours in a large basin, a dark blue pulverulent substance is 
gradually deposited, which, being collected on a filter and washed with 
alcohol, yields a body in all its properties fully identical with indigo-blue. 
The quantity so obtained varies from 10 to 20 per cent, of the weight of the 
isatine employed. The authors enter at great length into collateral matters 
of interest as regards the synthesis of indigo-blue ; but unless we were to 
produce a series of complicate formulas, we could not give any useful abstract 
of that portion of their paper. 
Researches on Alizarine. — A paper on this subject, which is now becoming 
popular enough among chemists, appears frbm V. Wartha in the Berichte 
der Beutschen Chemischen Gesellschaft zu Berlin, No. 12. The author states 
that, being engaged with researches on Turkey-red dyeing, he has found that 
the peculiarly brilliant red colour known by this term is due to a peculiar 
combination of alizarine with a fatty acid, which compound is soluble in a 
mixture of ligroine and ether, and does not even adhere very strongly to the 
cloth, since it may be readily removed therefrom by the liquid mixture 
alluded to. On evaporating this solution, there is left a brilliantly scarlet- 
coloured fatty substance, which, only after having been fused with caustic 
pot&saa, exhibits the characteristic reactions of alizarine. The author also 
states that the preparation of alizarine from madder is readily performed by 
first exhausting the substance (madder) with ligroine (light petroleum oil), 
and next treating it with a mixture of alcohol and hydrochloric acid (alcohol 
