48 _ M. Grotthus on the } (Jan. 
these last solutions, alcohol throws down the hydrate in yellowish 
white flocks.* 
The alkalies and the non-oxidizing acids, when no oxygen 
can interfere, appear incapable of producing any effect upon the 
metallic anthrazothionhydrates. 
Sect. 13. Anthrazothionate 9f Iron.—This compound when 
seen by transmitted light appears blood-red ; by reflected light it 
appears quite black, though now and then it shows a dark green 
metallic lustre on the surface. It deliquesces in the air, and 
cannot be obtained in the state of crystals. Acids deprive it of 
its iron oxide, and alkalies of its acid. In both cases the peculiar 
colour which distinguishes it disappears. It is exceedingly 
soluble in absolute alcohol, which enables us to obtain it in a 
state of great purity; it has a disagreeable, styptic, metallic 
taste. This property which anthrazothionic acid has of striking 
a strong red colour with oxide of iron renders the anthrazothion- 
ate of potash a very useful reagent for detecting the presence of 
that-‘metal. Jt is incomparably a more delicate test than prus- 
siate of potash, though not quite so delicate as the infusion of 
nut-galls. When an alkaline carbonate is present in a mineral 
water together with carbonate of iron, as is the case in Gelenauer 
water, in that case neither anthrazothionate of potash nor prus- 
siate of potash is capable of detecting the presence of the iron ; 
we must, therefore, in the first place, neutralize the carbonate 
by means of a stronger acid; then the liquid will strike a red 
colour with anthrazothionate of potash. ‘The red colour of an- 
thrazothionate of iron, when applied to organized bodies, as skins, 
paper, linen, wool, silk, is very fugitive, because the acid gra- 
dually makes its escape. Perhaps it might be fixed by means 
of a mordant. 
Sect. 14. Constituents of Anthrazothionhydrate of Copper.— 
This compound is formed when anthrazothionate of potash is 
mixed with a solution of copper and a disoxidizing body, as, for 
example, sulphate of iron is added to the mixture. From the 
origin of this white, bulky precipitate, described by Porvett, it 
seems to follow that the hydrogen in the acid is not sufficient to 
convert the whole oxygen of the oxide into.water. Hence the 
reason why the assistance of a disoxidizing substance is necessary 
for the formation of the hydrate. Porrett considers this com- 
pound as an anthrazothionate of copper, and states its consti- 
tuents at 36°855 acid and 63:145 oxide of copper. But. it 
contains a notable quantity of water, though Porrett affirms the 
contrary, even when it has been long dried in.as high a temper- 
ature as it can be exposed to without altering its w/ite colour 
(which would indicate a decomposition); for when it is heated 
* The properties of the anthrazothionhydrate of copper have been already 
described by Porrett, 
