1888 - 89 .] Mr John Aitken on Dust Particles. 
143 
Turning now to the first plan, fig. 1 is an elevation of the 
apparatus, fig. 2 a plan in section, fig. 3 an end elevation. These 
are all drawn to a scale of half size. Tig. 4 is a full size section of 
an important part of the apparatus. The letters in the different 
figures all correspond. AA is a pipe through which the air to he 
tested is caused to circulate, B is the measuring cylinder, CC is a 
pipe connected at its lower end with the chamber D and a filter E. 
When in use CC is connected at its upper end with the test-receiver 
by means of a short length of indiarubber tube (see Plate I.). E 
is a stopcock situated, as shown, between A, B, and C. The plug of 
this stopcock has the passage through it bored at right angles as 
shown, and not straight through, as is usually the case. The 
working of this arrangement will he most easily understood from an 
examination of the full size drawing, fig. 4. It will be seen that 
when the plug is in the position drawn, the air-pump B is in 
connection with the pipe carrying the air to he tested, and if the 
piston be drawn out the cylinder will get filled with this air. If 
the stopcock he now turned one quarter round, the pump will he 
put into connection through the stopcock with the pipe C ; and if 
the piston be now pushed down, the air in the cylinder will be sent 
by the pipe C into the chamber D, its passage upwards being checked 
by the stopcock on the receiver. From D the measured quantity of 
dusty air is drawn up through C and carried into the receiver, its 
place being supplied by filtered air from E. 
The cylinder B has a capacity of 10 c.c., and by means of it we 
can measure any quantity of air from ^ c.c. to 10 c.c. When more 
than 10 c.c. of dusty air requires to be sent into the receiver at one 
time, then the plug of the stopcock is turned one quarter farther 
round. By this means the pipe C communicating with the receiver 
is put into direct connection with the pipe A, and the air to be 
tested can be drawn direct from A into the receiver. The method 
of measuring when the plug is in this position, and when quantities 
larger than 10 c.c. are required, will be explained further on. 
The points to be aimed at in the construction of the part of the 
apparatus shown at fig. 4 are — first, to have the plug of the stopcock 
as small as possible with the requisite tightness. As there is never 
much pressure on it, a great amount of “cover” is not necessary. 
The plug sketched is large enough. The object of having a small 
