COD-LIVER OIL. 
651 
contains no artificially added iodine, the iodine which is naturally 
contained in, and more intimately combined with the oil, may be 
frequently recognized by another process. Marchand* gives the 
following directions for detecting it: Saponify the oil with soda, 
carbonize the soap thus obtained, digest the coal in distilled water, 
add a drop of starch paste, and subject the mixture to the action of 
a voltaic battery, the positive pole being placed in contact with 
the starch paste, the negative pole with the solution. If iodine be 
present, the starch becomes blue. Marchand states, that by this 
test the iodine can be detected in the urine of a patient soon after 
he has taken the oil. This, however, is certainly not always cor¬ 
rect, for I submitted the urine of a young gentleman, who for 
several weeks had taken with great benefit a table-spoonful of 
cod-liver oil thrice daily, to the action of a galvanic battery of fifty 
pairs of plates for several hours, without obtaining the slightest 
evidence of the presence of iodine. 
Sulphuric acid has been employed as a test for cod-liver oil. If 
a drop of concentrated sulphuric acid be added to fresh cod-liver 
oil, the latter assumes a fine violet colour, which soon passes into 
yellowish or brownish-red. Some samples of oil produce at once 
the red colour, without the preliminary violet tint. Gobley t who 
noticed this re-action in the case of oil of the liver of the ray, says, 
that oil which has been prepared by ebullition in water, does not 
possess this property, but yields with sulphuric acid a clear red 
colour. This, however, is an error, at least with respect to cod- 
liver oil. It has been erroneously supposed by some persons that 
this violet colour was due to the evolution of iodine by the action 
of the acid on an alkaline iodide contained in the oil. If that were 
the case, the presence of a little starch paste would be sufficient to 
convert the violet into an intense blue colour ; which is not the 
case. The colouration, in fact, depends on the action of the sul¬ 
phuric acid on some one or more organic constituents of the oil, 
and the following facts lead me to infer that it is in part due to the 
presence in the oil of one of the constituents of the bile. 
It is well known that in 1844, Pettenkofer f pointed out a new 
test for bile. If to a liquid supposed to contain bile, about two- 
thirds of its volume of oil of vitriol be added, the liquid kept cool, 
a few drops of a solution of cane sugar (four or five parts of water 
to one of sugar) be added, and the mixture shaken up, a violet red 
colour is produced, provided bile be present. This test succeeds 
* Lebrbuch der Physiolog. Chemie. 
t Journal de Pharmacies 3me ser., t. v, p. 308. 1844. 
+ Ann. der Chemie und Pharmacies Bd. lii, s. 90, 1844; also Simons 
Chemistry, translated by Dr. Day, vol. ii, p- 193. 
