RESULTS OF PHYSICAL AND CHEMICAL INVESTIGATIONS. 
121 
It is therefore named by Dr. Guthrie the Iodide of Iodammonium. 
This body is readily formed in the following manner:—A saturated solution of some very 
soluble salt of ammonia (the nitrate or carbonate) is treated with about one-third of an 
equivalent of hydrate of potash, so that all the potash is neutralized and the ammoniacal 
salt is in excess. To the clear solution finely powdered iodine is added in small quan¬ 
tities, with constant agitation. The iodine appears to be immediately and perfectly 
liquefied ; no appreciable heat is evolved. The resulting compound presents itself as a 
thoroughly mobile brownish-black liquid. The supernatant saline solution remains almost 
colourless. A few bubbles of gas rise from the lower liquid and drag portions of it to 
the surface of the upper one. The iodine is used in deficiency to ensure its complete 
conversion. The iodide of iodammonium is separated by a pipette from the saline 
solution. Its properties are briefly as follow:—• 
Exposed in a dry state to the air, it decomposes spontaneously into ammonia and iodine, 
no other gas being evolved. On agitating it in a eudiometer tube with mercury, iodide 
of mercury is formed, and the mercury is depressed by the liberated ammonia, -which 
latter is completely absorbed by water. 
NH 3 I 2 -f 2 Hg=NH 3 4- Hgl. 
Treated with water, it is decomposed, colours the water reddish-brown, evolves a per¬ 
manent gas, and gives rise to a residue which explodes spontaneously under the water. 
A few grammes of the iodide of iodammonium in a capsule being placed under water in 
a basin and covered with an inverted test-tube of water, a gas collects in the tube, 
which, after washing to remove ammonia, is found to be pure nitrogen. 
2NH 3 I„ 4- HO = NHL + NII 4 I 4- HI + HO 
== N -f 2 HI -f I -f NH 4 I 4- HO. 
The coloration of the water is due to the solution of the iodine in the hydriodic acid 
and iodide of ammonium. The formation of the biniodammonia (iodide of nitrogen) is 
more rapid than its decomposition, so that some of it is left after the original compound 
is completely broken up. 
The caustic alkalies effect the same decomposition as water, but act more energetically 
on account of the greater affinity of their metals for the iodine. 
Acids determine the formation of ammonia. 
NH 3 I 2 4- HC1 = NH 4 C1 4-1 2 . 
This change furnishes the means of analysis. 
The iodide of iodammonium dissolves in ether, bisulphide of carbon, alcohol, and 
solution of iodide of potassium. On being heated, it is partly decomposed into iodine 
and an iodiferous liquid, which may be distilled without change, and is probably 
NH 3 I or 3 NH 3 ,I 2 . 
Methods for Testing the Purity of Alcohols and Ethers. It is well known, 
that compound ethers are always liable to contain small quantities of water and of al¬ 
cohol, even when they have been carefully rectified and dried. Alcohols also frequently 
contain traces of compound ethers. These impurities are difficult to separate and often 
not easily detected. M. Berthelot gives the following elegant and efficient means for 
their recognition:— 
“1. I take as a starting-point the fact that a compound ether, if pure, is decomposable 
by an alkali, by saturating an equivalent weight of this alkali. By this means, as I 
showed about ten years ago, the analysis of ethers and analogous compounds is founded 
on an alkalimetric test, based on the use of a standard solution of baryta. 
“ 2. By means of the same liquid the smallest quantities of compound ethers may be 
recognized and estimated in alcohol or in simple ethers, provided these bodies are not 
alterable by alkalies. Ten cubic centimetres of a standard solution of baryta, and a 
known weight of the body to be tested, are enclosed in a flask. It is then heated for 
about a hundred hours at 100°; if the alcohol is pure, as is oftenest the case with or¬ 
dinary alcohol, the standard of the baryta does not change. Amylic alcohol, on the 
