SCIENTIFIC SUMMARY. 
235 
potash. The results, he adds, have a particular interest, since they serve to 
explain the difference of opinion expressed by chemists, some having asserted 
that dilute acids decompose the iodide, while others have denied that any 
decomposition takes place. 
The Proportion of Oxygen in certain Specimens of Air. — At a late meeting 
of the Manchester Literary and Philosophic Society, Dr. Angus Smith read a 
very interesting paper on this subject. The specimens of air contrasted were 
from St. John’s, Antigua, and from one of our own law courts. The sub- 
joined table shows that the latter specimen contained nearly *5 per cent, less 
of oxygen than the former : — 
OXYGEN PER CENT. IN SOME SPECIMENS OF AIR. 
18 ft. above water. Pine day. 
2’30 p.m. 
Lat. 43*05, W. 17T2. 
21-0100 
21-0000 
20-9700 
St. John’s, Antigua. 
April 11th, 1865. 9 a.m. 
Showery morning. 
20-9600 
20-9100 
210000 
Mean 20 "99.90 
Law Court, Feb. 2, 
1866. 
20-6400 
20-6700 
Mean 20*9950 
Law Court, from the 
lantern, 4.30 p.m., just as the 
Court was closing. 
20-5000 
20-4800 
Mean 20-6500 
Mean 20-4900 
Paraffin in the Preservation of Frescoes. — In Dingier 1 s Journal et Bulletin 
de la Societe Chimique it is stated that paraffin may be used with advantage 
for the above purpose. Vohl coats the picture with a saturated solution of 
paraffin in benzole, and when the solvent has evaporated, washes the surface 
with a very soft brush. Paraffin has this advantage over other greasy 
matters, — it does not become coloured by time. — Vide also Chemical News. 
Danger in Preparing Potassium-Ethyl. — It may be well for young chemists 
to know that though there is no great danger to the operator in preparing 
the sodium compounds of ethyl or methyl, the preparation of the potassium 
compounds of these radicals is attended with considerable risk. It is stated 
by Dr. Wanklyn, of the London Institution, that when the replacement of 
the zinc by the alkali metal proceeds briskly, there is a considerable rise of 
temperature both in the case of sodium and potassium. From the low tem- 
perature at which potassium fuses, it very easily happens that the potassium 
fuses ; and when once this occurs, a most tremendous explosion is the imme- 
diate result. 
The New Ancesthetic Chloro-carbon can be made from chloroform, by 
passing chlorine into it ; and it has been shown by Geuther that the process 
can be reversed — that chloroform may be produced from chloro-carbon, by 
treating it with zinc and dilute sulphuric acid, and then exposing it to the 
action of nascent hydrogen. The most common way hitherto adopted of 
forming bichloride of carbon consists in passing the vapour of bisulphide 
of carbon, together with chlorine, through a red-hot tube, either made of 
R 2 
