124 ON THE SO-CALLED “ INACTIVE ” CONDITION OF SOLIDS. 
the Disengagement of Gases from their Saturated Solutions,” in which it is stated that 
on stirring up seltzer-water or an aqueous solution of carbonic acid with a solid rod, the 
rod loses its property of disengaging bubbles of gas after some time, and that the im¬ 
mersion of the body in water, the action of heat, and shelter from the air also render it 
inactive. 
Some interesting experiments on this supposed inactive condition of matter were 
made by Herr Ziz, of Mayence, as long back as the year 1809, and were recorded by 
Herr Schweigger in 1815.* Tt was found that bits of iron-wire, flint, glass, small 
coins, etc., cause supersaturated solutions of sulphate of soda to crystallize by acting as 
nuclei to which the crystals can attach themselves; but if previously wetted these 
bodies become inactive. If thrown dry into a hot solution, and allowed to cool with it, 
they are also inactive, and may be shaken up in the solution without producing any 
effect. Air artificially dried was also inactive; but ordinary air produced crystallization 
(as it was thought) by introducing particles of dust. A dry nucleus that had been 
exposed to the air immediately produced crystallization ; but if driven through the cork 
so as to touch the supersaturated solution it did not induce crystallization. A knitting- 
needle is given as a convenient illustration of this phenomenon. The most efficient 
nucleus in inducing crystallization is a crystal of the salt itself ; but the efflorescence 
from a solution into the neck of a phial contained in a large flask in which the air was 
dried by means of caustic potash, was repeatedly redissolved by agitating the vessel 
without inducing crystallization. An open vessel containing a supersaturated solution 
will remain liquid if lightly covered, as with a watch-glass. Ziz distinctly recognized 
the existence of two varieties of sulphate of soda with different fusing-points. Indeed, 
the paper is in advance of the time at which it was written, and its merit has not, I 
think, been sufficiently recognized. 
M. Henri Leowel has published a number of memoirs on supersaturated solutions,f 
in which he recognizes the distinction between active and inactive solids, or, as he terms 
them, dynamic and adynamic , in inducing crystallization ; and he is of opinion that the 
cause of the difference is not mechanical but catalytic. He found that if a glass rod be 
heated to 30° or 40° C. it could be used for stirring up a supersaturated solution with¬ 
out inducing crystallization. Rods of copper, iron, and zinc were passed through the 
corks used for closing flasks containing boiling solutions. As the solutions cooled, 
vapour condensed on the metal rods, which became dry in two or three days, the iron 
being oxidized, but they were all inactive. Metal rods heated to 100° C. in boiling 
water or otherwise were also inactive ; if heated to from 150° to 200° C., and left to cool 
under cover, they became inactive ; but if exposed to air for some time, they resumed the 
active condition in a quarter of an hour, or from that to an hour. Rods of glass, etc. 
kept in cold water become partially or wholly inactive, but regained their activity by 
exposure to the air so as to evaporate the water. The author does not pretend to ex¬ 
plain these phenomena, but speaks of “ that mysterious action ” which the air and other 
bodies exert in inducing crystallization. 
I think it would not be difficult to show that this so-called “ inactive ” condition of 
solid matter is simply a question of adhesion. The bits of iron-wire, flint, glass, small 
coins, etc., in their dry state induce crystallization because there is adhesion between 
them and the supersaturated solution; that is, they are wetted by the solution ; but if 
previously wetted with water they are not wetted by the solution when thrown into it, 
and consequently cannot act as nuclei , because the solution does not really come in con¬ 
tact with them. In like manner, a glass rod made chemically clean will act differently 
from a rod that has been exposed to the air: the latter is said to be in an “ active ” 
condition ; what, then, is the former ? Is it “ inactive ” because it does not always do 
the work that is expected of it ? But it may do other work, and prove itself a more 
efficient agent than the so-called “ active ” rod. This is particularly the case with the 
interesting experiments on the supersaturated solutions of gases already referred to. But 
what are the facts ? A glass rod or other solid body put into soda-water or seltzer- 
water disengages gas, provided it has been previously exposed to the air, but not other- 
* “Ueber den Einfluss des Luf'tdruckes auf Krystallisation der Salze,” ‘Journal fiir 
Chemie und Physik,’ vol. xv. pp. 160-171. 
f The first memoir, “ Sur la Sursaturation des Dissolutions Salines,” is contained in the 
‘ Annales de Cliimie et de Physique ’ for 1850. 
