ON THE THEORY OF SOLUTION. 337 
be brought into the dissociated or electrolytic condition. The compound 
is interesting, since water and alcohol produce well-known and remark- 
able actions’ upon it; moreover it is comparatively easily prepared in the 
pure state. It appears from the paper referred to that stannic chloride 
ean be mixed with chloroform without receiving any conducting power. 
It will also absorb a considerable quantity of dry H,S gas without chemical 
action, and again without becoming electrolytic ; whereas the addition of 
a drop of water or alcohol to the non-electrolytic mixture immediately 
gives rise to chemical action with a deposit of tin sulphide, the liquid 
becoming at the same time electrolytic. 
The action of water or alcohol seems to be clearly different in this case 
in some fundamental manner from that of H,S or chloroform. 
Mr. Shaw also drew attention to the diagram (fig. 1) in Mr. Picker- 
ing’s paper, from which, if he understood it correctly, it appears that for 
very weak solutions the ‘ molecular depressions’ produced by certain salts 
are the same for solutions containing ‘08 molecule per 100H,0 as they 
are for infinitely dilute solutions. 
Mr. Pickerinc remarked that there were very strong positive argu- 
ments in favour of the hydrate theory, and that his opponents had in no 
way controverted them. Even if they succeeded in refuting all the 
objections which he had raised against the physical theory, this theory 
could not be established till it was shown that other theories were either 
untenable or less satisfactory. 
The freezing-points of sulphuric acid solution calculated by Arrhenius 
certainly showed a very striking agreement with the observed values; but, 
before attributing much weight to this agreement, it would be necessary 
to examine carefully the details of the calculations, for there are consider- 
_ able sources of doubt and difficulty in applying the values for the conduc- 
tivity of weak sulphuric acid solutions ; but even if no exceptions could 
be taken to the calculations, it must be remembered that the agreement 
exhibited extended only up to 1 per cent. solutions, or 0°-4 depression, 
whereas, according to the values quoted above, his theory offered an 
equally good agreement up to 30 per cent., or 34° depression, and, accord- 
ing to values given elsewhere, a similar agreement extended, with certain 
exceptions, up to 94 per cent. It must also be remembered that according 
to the chemical as well as the physical theory there must be a mathemati- 
eal connection between the freezing-points, conductivities, and all other 
properties of solutions. The freezing-point curve shows irregularities, 
and so also does the conductivity curve; the chemical theory explains 
these irregularities, whereas according to the physical theory they should 
not exist. 
Professor van ’t Hoff pointed out that according to his theory the 
freezing-points were influenced by the nature of the solvent; but this 
does not remove the objection that the nature and amount of the dissolved 
substance (even when this is a non-electrolyte) are found to influence the 
results. Professor van ’t Hoff had misunderstood what had been said 
about Raoult’s constant: he (Mr. Pickering) was well aware that this 
constant and that deduced in the osmotic pressure theory were quile 
different. 
Professor Ostwald stated that his experiment of bringing a charged 
body up toa solution, dividing the latter, and removing the charged bodv, 
ig. ad analogous to a similar operation performed on a metallic 
: Z 
