FALSIFICATION OF PRECIPITATED CHALK. 
307 
ly rapid passage of the fluid, and all the other inconve- 
niences may, it seems to me, be obviated simply by regula- 
ting the rapidity of its flow by means of the stop cock. 
The operator should keep in mind the swelling of the dry 
materials when penetrated by the menstruum, and guard 
against the too great compactness which might thus be pro- 
duced. To this end let the maceration be performed be- 
fore putting the materials into the displacement vessel. 
Be sure that the flow of the fluid from the displacement cy- 
linder is not much more rapid than its subsidence through the 
most compact part of the mass, and you secure the great 
object of subjecting every part of the mass to the action of 
each successive stratum of the fluid. 
Lastly, let the flow be by such slow degrees as to give 
time for the solvent action of the fluid, and the great ad- 
vantages of the process of displacement are attained. 
When a fluid of less density is to be displaced by one of 
greater density, there will be, to a greater or less extent, 
an admixture of the two : in such a case it would be pro- 
per to give more attention to the pulverization and packing 
of the material. 
I do not know that there is any thing of novelty in these 
suggestions : indeed, I suppose many, like myself, have 
long employed in practice the principle which they involve. 
I have nevertheless thought it proper to offer them for con- 
sideration. 
ART. LXVm.— FALSIFICATION OF PRECIPITATED CHALK. 
By Richard H. Stabler, M. D., of Alexandria, Ya. 
Having my attention accidentally arrested by a fraudu- 
lent substitution for an important article which, if it pre- 
vails to any extent, may have an important bearing on the 
