OF MICROSCOPIC OBJECTS. 187 
appearing almost black; yet by transmitted light no colour 
is more useful, because its distinctness is equally great by 
artificial light and ordinary daylight. The method of pre- 
paring this, as given by Dr. Beale, is as follows :— 
GEEVCOTUIGS .. ven enon scessrsiseaecapacanes baaas?* LrOmnee. 
Wood naphtha, or pyroacetic acid ...... 1$ drachm. 
SPM OL WIHE! 2) cc cisdecacsacccnedorsaccas 1 ounce. 
Ferrocyanide (yellow prnssiate) of potas- 
POP san dieRavddavscmansies ndsee \iadaes dock . 12 grains. 
Tincture of sesquichloride of iron......... 1 drachm. 
DN i Mec clec a cunaiarnnanndascensh choc smasss, v4 OUNeaR 
Dissolve the ferrocyanide of potassium in one ounce of the 
water; add the tincture of sesquichloride of iron to another 
ounce, Mix these solutions gradually together, shaking the 
bottle well which contains them—it is best to add the iron 
to the potash solution. When thoroughly mixed, these 
solutions should produce a dark-blue mixture, perfectly 
free from any perceptible masses or flocculi. Next mix the 
naphtha and spirits of wine, and add the glycerine and the 
remaining two ounces of water. This must now be slowly 
mixed with the blue liquid, shaking the whole well in a 
large bottle whilst the two come together. The tincture of 
sesquichloride of iron is recommended, because it can always 
be obtained of a uniform strength. 
31. Dr. Turnbull used a mixture slightly different from 
the above, which is made with the sulphate of iron :— 
Purified sulphate of iron ............08. 10 grains. 
Ferrocyanide of potassium ...........0.6 32 grains. 
J EE es 1 ounce. 
DPE I a. aca cic icasveccecnes 13 drachm. 
PN eae eo a ciate. ne ncinin de - 1 ounce. 
IES RE SORE, OY 5 TS ee Oe ee 4 ounces. 
Dissolve the sulphate of iron in one ounce of the water, 
