THE METHODS OF MICROCHEMICAL QUALITATIVE ANALYSIS 313 
When a precipitate is to be recrystallized from hot concen¬ 
trated sulphuric acid, it must be placed or formed at the corner of 
the object slide and any supernatant aqueous solution decanted. 
A moderate sized drop of the concentrated acid is then placed 
upon the precipitate and the slide immediately inclined at an angle 
of at least 30 degrees, to prevent the acid from spreading. Heat 
from a tiny flame is then applied to the object slide just below 
the upper edge of the drop, and as the acid fumes off the flame 
is brought nearer and nearer to the corner. As soon as it appears 
that sufficient material has passed into solution, the preparation 
is removed from the flame and allowed to cool for a few seconds, 
while still held in an inclined position. The inclined slide is then 
tipped so as to cause a slow flow to the adjacent corner (see page 
280, Decantation), thus decanting the clear acid from the remain¬ 
ing insoluble precipitate, the channel of flow is cut off with filter 
paper and the slide inclined until it is almost vertical, thus 
causing the clear drop of acid to gather at the very corner of the 
slide. This corner is then touched to a clean slide and through a 
touch with a glass rod or platinum wire the drop is made to flow 
from the inclined slide to the horizontal one. A small clear drop 
is thus obtained. 
This system of attack can be employed in all cases involving 
re-solution in strong reagents. Where constituents dissolving 
from the glass slide are objectionable platinum foil can be em¬ 
ployed, eventually transferring as above to a glass slide. 
The second case mentioned arises most often in the analysis 
of organic compounds, as, for example, in the separation of a 
free base from its salts by means of an alkali. Although the 
amorphous appearing material will eventually crystallize sponta¬ 
neously if given sufficient time, it is usually desirable to hasten 
the formation of typical crystals. This can be accomplished by 
taking upon a platinum needle the most minute fragment 
possible from a portion of the pure base believed to be present 
and drawing it through the amorphous mass, crushing it at 
the same time. Crystallization of the amorphous material is 
almost always immediately started and proceeds with great 
rapidity. 
