50 On Subdivision by Trituration and Solution. 
pestle will either be so thin as to elude its dividing action, or so 
thick that the number of parts which are pressed against each 
other by its strokes and reunited, will equal the number divided 
by the same strokes. At this stage, the comminution will cease ; 
and the trituration, ever so skillfully conducted, and carried on 
forever, could not "reduce: the powder to any greater degree of 
Is there any way in which this limitation may be obviated, 
and the fineness of the powder indefinitely increased? Yes: it 
may be done by successive mixtures with some other substance, 
using thorough os after adding ~_ portion. This meth- 
is of universal application; yet for the sake of convenience 
wad precision, I shall assume particular duane and a particu- 
lar proportion. Suppose a flint powder to be rendered as fine as 
it is possible to make it by rubbing it per se; and suppose one 
grain of this to be triturated with ninety-nine grains of ordinary 
loaf-sugar, or of the harder—and therefore better—non-medicinal 
a spoon or spatula, the flint powder be intimately mixed with 
the pulverized sugar, so as to be uniformly distributed through it, 
before the trituration is commenced. ['This is not requisite in 
practice, but simplifies the escrito, Then each of the mi- 
croscopie flint stones is surrounded by ninety-nine times its weight 
of sugar, which keeps them at nearly five times their former dis- 
tance from each other, as estimated from centre to centre. Wh 
is the consequence, if trituration be commenced under these cir- 
cumstances? A new and far more minute division must result. 
The sugar serves two purposes, viz. first, to divide the flint, 
and secondly, to keep it divided ; it contributes both to effect and 
preserve the division. It serves the first of these purpeses in 
more than one way. First, it aids division by mechanical collis- 
ion, When driven against the flint by the pestle. It in this way 
aids the fracture; as the stroke of one body may often be made 
to break another ‘though harder than itself. Thus a quartz peb- 
ble can be crushed between two large pieces of marble, and a still » 
smaller one between two large pieces of sugar of milk. . The ad- 
vantage given by magnitude, suggests that the sugar employed 
will be more effectual if ncloatind: in a state coarser than that of 
the harder powder which it is employed to comminute. In later 
_ stages it will necessarily have this advantage. Secondly, the su- 
may aid the division by its affinity, its attraction for the flint. 
Thus whilst some of the pieces of hard sugar are acting as ham- 
mers and wedges, and tending to separate an intermediate piece 
of flint into two pieces, other pieces of sugar, situated in the line 
bed which the fi ragments of flint when divided tend to move, may » 
eir affinity draw the fragments in the direction in which the 
other pieces of sugar push them, and thus both kinds of force 
conspire to effect their separation. eave 
