REPORT ON NEW FERRUGINOUS PILLS. 249 
fall of the liquid through the air is sufficient to produce it. 
The quantity of sulphuric acid necessary, is very small, about 
a drop, or a drop and a half, to each ounce of the concentrated 
boiling solution, is more than sufficient; and it is useful, also, 
to moisten the beak of the funnel externally with the acid, 
because, if this be not done, the liquid becomes turbid around 
it. It is equally necessary to agitate the solution from time 
to time, so that the sulphuric acid may be uniformly mixed 
through it. 
Upon cooling, the salt crystallizes, and it can be obtained 
at will, in large or small crystals; it is much more advantage- 
ous to have it in small crystals, because it is easier to dry, 
and also dissolves more readily in water. In this case the 
solution, while crystallizing, is disturbed by slight agitation; 
and, if the liquid be cooled by ice, a greater quantity of 
crystals are obtained. The crystals are finally placed upon 
filter paper in a funnel; as soon as the liquid has drained 
from them, they are exposed upon unsized paper and covered 
with the same, pressing the paper down upon them; this is 
done several times, until the salt is perfectly dry. 
The following are the properties of the pure salt obtained 
in this manner. Its color is not green or bluish green, as is gene- 
rally the case with this salt, but rather blue, approaching some- 
what to green; it is of the beryl blue shade, — less green than the 
stone known as aqua marina. Should itassumea green color,or 
become more green than blue, it can be pronounced with cer- 
tainty that it already contains a sesquioxide; the color is, in fact, 
the most sensible test of purity in this respect; and the best 
mode of determining this is to compare it with the pure salt. 
When effloresced in dry air, a white powder is formed, as 
pure as that of chloride of mercury in powder. But with 
time, at the end of several weeks for example, the color com- 
mences to pass gradually to a light yellowish green. If this 
powder is then dissolved in water, the solution is rendered a 
little turbid by an ochreous deposit, which is, as is known, 
the basic sulphate of the sesquioxide of iron, indicative of 
decomposition produced by the air. 
