4 
MACHINE FOR MAKING BLUE MASS. 9 
visible to the eye. The whole was then kneaded as bread 
dough for a few minutes, and divided into four portions, each 
seven and a half pounds, one of which was put into the cylin 
derand operated on with the single knife piston for twenty- 
five minutes, when it was removed, and another charge 
introduced in the same manner. This was repeated on 
each of the other quarters for the same time. By this third 
treatment the mass had acquired the ordinary colour of blue 
mass, though not so dark as usual ; the mercury was invi- 
sible to the unassisted eye, and but slightly with a common 
lens. The quarters were again sub-divided as before, and 
the machine kept in motion for half an hour on each fourth, 
the single knife being used. The mass now had the proper 
bluish-grey colour, was smooth and uniform in texture, and 
when examined with a lens, but slight traces of mercury 
globules were visible, not more than are frequently obser- 
vable with a glass of the same power, in the commercial 
mass. The inventor was of opinion that the mass should 
be treated once more for half an hour on each quarter, 
which was accordingly done, when he pronounced the mass 
finished. Owing to the method adopted of operating on 
one-fourth at a time, the actual period during which the 
machine was in motion in finishing the whole 30 lbs. ex- 
ceeded that prescribed by the inventor, amounting in all to 
nine hours, but if the delays occasioned by removing the mass 
be added, the time will be 3 hours more. But the actual 
time required to have finished any fourth of it would be 
3 hours and 45 minutes. The reason for operating on a 
fraction was that the power of one man is insufficient to 
turn the crank axle, with the whole quantity in the cylinder, 
and if the power is applied to the other axle, the motion of 
the piston is too slow to affect the object within the time 
specified. 
Jlnalysis. — The products of the last four operations of the 
machine were each submitted to analysis by the plan of Dr a 
