250 DAVIES, ON CRYSTALLIZATION 
I. SANTONINE. 
I have chosen santonine as the first to be considered. 
This substance is procured by boiling seeds of the artemisia 
and dry lime in alcohol; the decoction is then distilled, 
filtered, evaporated to one half, and afterwards boiled in 
an acid solution. When cold the santonine crystallizes in 
feathery forms, and after washing in alcohol is redissolved, 
and again crystallized. This salt is but sparingly soluble in 
water; but at 338° Fahr. it melts, and if the heat is not raised 
much higher than this point, and is carefully applied, no 
decomposition or change of colour occurs. 
To prepare microscopic slides of this beautiful salt a satu- 
rated solution may be made in alcohol, then spread upon the 
slide, and the liquid evaporated. But this mode of pro- 
ceeding is very inferior in the uniformity of its results to 
fusion, which may be effected as follows :—A small portion 
of the salt must be placed upon the centre of the slide, and 
the whole of the slide heated until the santonine is fused. 
By the aid of a hot needle the substance must then be evenly 
and thinly spread upon the surface required. As the tem- 
perature is lowered the formation of crystals, in various 
parts of the plate, takes place until the whole fused mass is 
covered. These crystals should be then mounted in castor 
oil, as santonine is slightly soluble in the Canada balsam 
which is ordinarily met with. Should, however, the diffi- 
culty in using oil prevent the operator from attempting it, 
he may safely use balsam if the film of santonine be a thick 
one, and the balsam be no deeper upon the salt than is abso- 
lutely necessary. Thus, the coating of balsam will become 
saturated with the salt without seriously damaging the crystal, 
provided the balsam be pure. But it may be here mentioned 
that, as it is usually obtained, it is not unfrequently adul- 
terated, turpentine and other solvents being added to the 
stock lest it should become hard and useless. ‘These solvents 
readily dissolve many substances which remain uninjured 
in pure balsam, and thus crystals and other objects are 
frequently lost, and the true action of balsam mistaken. 
In form the aggregated crystals of santonine differ accord- 
ing to the temperature at which formation takes place; but 
the salt is not really dimorphous. The changes are produced 
by relative position and size of crystals alone. The tempe- 
rature at which the salt is fused, however, has no influence in 
this particular, but too high a degree of heat during fusion 
frequently gives it a brown colour. 
st.205 >t Ge Pb * 
