52 Proceedings of Royal Society of Edinburgh. [sess. 
gauge by measurement the capacity of the space not emptied, when 
the piston of the pump is returned, to enable us to make the 
necessary calculations to find the number of particles. Perhaps the 
best way of gauging would be to test air which gave, say, five drops 
per square millimetre, when using ~ of impure air, and working in 
the usual way. Then test this same air and see how many it gave 
when using the contents of the small space above the piston. 
Perhaps it might give one drop per four square millimetres. If a series 
of tests give these figures as the average number, we would know that 
the capacity of the space was of the ~ measure, or the T oVo 
that of the receiver. So that whatever number we observed in the 
air of the receiver when working in this manner would require to 
be multiplied by 1000 to get the number in the air tested. 
The instrument is so constructed, that when the different parts 
are unscrewed they fit into a case 4§ inches by 2J inches by 1J 
inches deep, or little larger than a well-filled cigar-case. The 
weight of the instrument, without the case, is a little under 8 oz. 
On the Action of Metallic (and other) Salts on 
Carbonate of Lime. By Robert Irvine, F.C.S., and 
W. S. Anderson. 
(Read January 9, 1891.) 
It is well known that pseudomorphic changes take place with 
many minerals. These changes may be either by alteration or 
displacement. In the case of carbonate of lime they are generally 
of the former order. 
Among other work conducted at the Marine Station, Granton, 
during the past year, a number of experiments were instituted with 
the view of showing how far carbonate of lime was influenced in 
this direction by metallic and other salts. 
Corals, preferably the more porous and soft varieties, were 
selected for this purpose, and these were exposed to the action of 
solutions of the following salts : — Chloride of manganese, sulphate 
of iron, chloride of zinc, chloride of chromium, nitrate of nickel, 
nitrate of cobalt, nitrate of copper, nitrate of lead, chloride of 
mercury, chloride of tin, nitrate of silver, phosphate of ammonia. 
In many cases me action was very slow, especially in the case of 
