190 
Dr. Thomson on some of 
Atomic 
weight. 
Chromium - 4 
Green oxide 4 chromium 1 oxygen = 5 
Chromic acid 4 -f- 2 ‘5 =6*5 
Brown oxide4 + 1*2142857= 5-2142857 
Two atoms and a half, the proportion of oxygen united to 
an atom of chromium in chromic acid, has not yet been 
observed, except in the hyposulphuric acid of Gay-Lussac, 
which is a compound of 1 atom sulphur, and 2-5 atoms 
oxygen. 
IV. Chloro-chromic acid. 
I proceed now to describe the properties of a rather remark- 
able compound, which I discovered about a year and a half ago, 
and which, from the great energy with which it acts upon 
combustible substances, will be very acceptable to those per- 
sons who are fond of exhibiting brilliant chemical experiments. 
Chloro-chromic acid may be obtained with great facility 
by the following process. Triturate together in a mortar 
190 grains of bichromate of potash, and 225 grains of com- 
mon salt, till they are intimately mixed. Pour the dry 
powder into a tubulated retort : insert the beak of the retort 
into a dry glass receiver, fitting it by means of a perforated 
cork, which should not be quite air tight. Pour into the 
retort 500 grains of the sulphuric acid of commerce, and by 
agitation make it into a magma with the salts. Then apply 
the flame of a lamp to the bottom of the retort. An efferves- 
cence takes place, and beautiful red fumes soon make their 
appearance. These condense in the beak of the retort, and 
gradually drop into the receiver under the form of a red- 
