1877.] 



On Supersaturated Saline Solutions. 



523 



ping sparks pass between the terminals at more or less rapid intervals, 

 exactly like the sparks of a small Leyden jar. They pierce writing- 

 paper with minute holes. It is usually necessary to approach the ter- 

 minals to a distance of 0*3 inch, when the striking- distance of 8040 cells 

 is 0*34 inch, in order to produce this static discharge. 



It has been found that an accumulated charge of a condenser of 42*8 

 microfarads capacity, charged with the potential of 3240 cells, produced 

 neither an elongation nor a contraction of a metallic rod 0*2 inch when 

 suddenly discharged through. This charge deflagrates 10-5 inches of 

 platinum wire 0*0125 inch in diameter. 



More dense sparks were obtained with one of Apps's coils for pro- 

 ducing 6-inch sparks when the primary was connected with 1080, 2280, 

 3480 chloride-of- silver cells, than when it was used with a zinc-carbon 

 bichromate-of-potash battery of 6 cells, producing a current 300 times as 

 great, thus showing the influence of high potentials in inducing se- 

 condary currents. 



These currents of high potentials have also a marked effect in inducing 

 magnetism, when the actual current is taken into account. 



The second part of the paper, which is in course of preparation, will 

 deal with the discharge in rarefied gases, in the so-called vacuum tubes, 



December 20, 1877. 



Dr. ALLEN THOMSON, Vice-President, in the Chair. 



The Presents received were laid on the table, and thanks ordered for 

 them. 



The following Papers were read : — 



I. (( Notes on Supersaturated Saline Solutions." By Charles 

 Tomlinson, F.R.S. Received September 14, 1877. 



There is probably no subject in science that is more involved in con- 

 tradiction than that of supersaturation. All the phenomena connected 

 with it seem to behave differently in the hands of different inquirers, so 

 that the facts affirmed by one writer are simply denied by another • and 

 the same theory which seems to have been disproved by one is again and 

 again brought forward by another. 



Take one point by way of example, namely, the nuclear action of 

 bodies in producing the sudden crystallization of a supersaturated saline 

 solution. Ziz, in 1809, stated that not only air, but solids, act best as 

 nuclei when dry : if wet, or boiled with the solution, or thrown into it 



