SCIENTIFIC SUMMARY. 
81 
which he considers the salt to he in chemical combination with the ice. In 
1877 Pfaundler showed, from theoretical considerations, that the properties 
which Guthrie found the cr yohydrates to possess occur in the same way in 
the case of a mixture of ice and salt, and as such he regards the cryohydrates. Of 
the same view is H. Offer in a paper which contains the following conclusions 
against the existence of cryohydrates as chemical compounds. Against the 
possibility of a chemical combination existing in these bodies is the relative 
quantity of water found in them. The cryohydrates of NH 4 C1 contain 12'4 of 
water ; that of KC1, 16‘61 ; that of Na 2 C0 3 , 92’75 ; that of K 2 S0 4 , 114’ 2 of 
water, and so on. He finds throughout numbers which give expression to 
no stochiometric law, and with much greater probability indicate mechanical 
mixtures. Furthermore, there is the circumstance that no cryohydrate, when 
becoming solid, furnishes a distinct definite crystal, which, as is well known, 
is quite characteristic of a chemical compound, but yields in each case an 
opaque, entangled, crystallized mass. 
If cryohydrates are placed in alcohol, it is foimd that the ice is dissolved 
out of the substance, beginning of course with the outer layer ; and the salt 
remains asadownlike shell of the inner unchanged cryohydrate : only after longer 
action did the entire mass fall to pieces. If, on the other hand, a cryohydrate 
is placed in water, the outer layer is, first of all, changed into transparent ice ; 
this coating of ice increases at the cost of the cryohydrate kernel, step by step 
inwards, until at last the kernel vanishes, and a piece of ice the same size as 
the cryohydrate remains. Here the water has evidently gradually taken up 
the salt from out of the mixture. In the case of four different cryohydrates 
calorimetric determinations of the heat of solution were made, and the cooling 
observed in each case compared with those which, under similar conditions 
of temperature, salt and ice of the cryohydrate alone would furnish. In all 
experiments, the difference between the heat absorbed by the cryohydrates 
and by the constituents separately is so small, that they were within the errors 
of experiment, and may be estimated as nothing. Herr Offer determined 
the specific gravity of a number of cryohydrates, and compared them with 
that of their constituents, and in a whole series of cases found a pretty good 
accordance. 
These results, while not fully proving the cryohydrates to be mere mix- 
tures, yield results which, taken with the others above referred to, give to 
the assumption a great degree of probability. ( Sitzungsher . Wien. Akad. der 
Wiss. 1880. lxxxi. 1058.) 
Fire Extinction. — Some comparatives experiments have been made on a 
plot of ground adjoining the Savoy, Strand, with water and sodium silicate, 
as recommended by Herr Windsperger. Two piles of timber, 9 ft. long, 
7 ft. high, and 4 feet deep, were filled in with straw, well saturated with 
petroleum and benzol in equal quantities, and ignited. After burning 
for five minutes, operations were commenced by throwing water on one, and 
sodium silicate on the other, with a handpump. In the course of about one 
; minute the fire treated with the silicate was extinguished, while that treated 
with water did not give in till about four minutes. And it was further 
found that twelve gallons of the solution and twenty-two gallons of water had 
| been used. The results of the experiment were most conclusive. 
The Conditions attending Explosion. — It appears that when the rocket 
NEW SERIES, YOL. Y. NO. XVII. G 
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