no 
POISONS : THEIR EFFECTS AND DETECTION. [§ 83. 
is injected with black blood, and was filled with an acid, grumous 
matter. 1 
Looking at these and other museum preparations illustrating the 
effects of sulphuric and hydrochloric acids, it is difficult (in default of 
the history of the cases) to distinguish between the two, by the naked- 
eye appearances, save in those cases in which the disorganisation was so 
excessive as to render hydrochloric acid improbable. On the other hand, 
the changes produced by nitric acid are so distinctive, that it is im¬ 
possible to mistake its action for that of any other acid. The nitric 
acid pathological preparations may be picked out at a glance. 
Detection and Estimation of Free Hydrochloric Acid. 
§83. (1) Detection. A large number of colouring reagents have 
been proposed as tests for the presence of free mineral acid. Among the 
best is methyl-aniline violet decolorised by a large amount of hydrochloric 
acid , the violet turns to green with a moderate quantity, and to blue 
with a small quantity. 
Tropaeolin (00), in the presence of free mineral acid, strikes a ruby- 
red to a dark brown-red. 
Congo-red is used in the form of paper dyed with the material ; 
large amounts of free hydrochloric acid strike blue-black, small quan¬ 
tities blue. 
Giinzburg’s test is 2 parts phloroglucin and 1 part vanillin, dissolved 
in 100 parts of alcohol. Fine red crystals are precipitated on the 
addition of hydrochloric acid. To test the stomach contents for free 
hydrochloric acid by means of this reagent, equal parts of the fluid and 
the test are evaporated to dryness in the water-bath in a porcelain dish. 
If free hydrochloric acid be present, the evaporated residue shows a red 
colour , 1 mgrm. of acid can by this test be detected. The reaction is 
not interfered with by organic acids, peptones, or albumin. 
Jaksch speaks highly of benzopurpurin as a test. Filter-paper is 
soaked in a saturated aqueous solution of benzopurpurin 6 B (the variety 
1 or 4 B is not so sensitive), and the filter-paper thus prepared allowed 
to dry. On testing the contents of the stomach with the reagent, if 
there is more than 4 parts per 1000 of hydrochloric acid the paper is 
stained intensely blue-black ; but if the colour is brown-black, this is 
from butyric or lactic acids, or from a mixture of these acids with 
hydrochloric acid. If the paper is washed with pure ether, and the 
colour was due only to organic acid, the original hue of the paper is 
restored ; if the colour produced was due to a mixture of mineral and 
organic acids, the brown-black colour is weakened ; and, lastly, if due to 
hydrochloric acid alone, the colour is not altered by washing with ether. 
1 A drawing of parts of tho gullet and stomach is given in Guy and Ferrier’s 
Forensic Medicine. 
