92 POISONS : THEIR EFFECTS AND DETECTION. [§ 64. 
Wood almost immediately blackens, and the spot remains moist. 
Spots on paper become quickly dark, and sometimes exhibit a play 
of colours, such as reddish-brown ; ultimately the spot becomes very 
black, and holes may be formed ; even when the acid is dilute, the 
course is very similar, for the acid dries in, until it reaches a sufficient 
degree of concentration to attack the tissue. Small drops of sulphuric 
acid on a Brussels carpet}, which had a red pattern on a dark-green ground 
with light-green flowers, were found to act as follows : the spots on the 
red at the end of a few hours were of a dark maroon colour, the green 
was darkened, and the light green browned ; at the end of twenty-four 
hours but little change had taken place, nor could anyone have guessed 
the cause of the spots without a close examination. Spots of the strong 
acid on thin cotton fabrics rapidly blackened, and actual holes were 
formed in the course of an hour ; the main difference to the naked eye, 
between the stains of the acid and those produced by a red-hot body, 
lay in the moistness of the spots. Indeed, the great distinction, 
without considering chemical evidence, between recent burns of clothing 
by sulphuric acid and by heat, is that in the one case—that of the acid 
—the hole or spot is very moist ; in the other very dry. It is easy to 
imagine that this distinction maybe of importance in a legal investigation. 
Spots of acid on clothing fall too often under the observation of all 
those engaged in practical chemical work. However quickly a spot of 
acid is wiped off, unless it is immediately neutralised by ammonia, it 
ultimately makes a hole in the cloth ; the spot, as a rule, whatever the 
colour of the cloth, is of a blotting-paper red. 
Sulphuric acid dropped on iron attacks it, forming a sulphate, which 
may be dissolved out by water. If the iron is exposed to the weather 
the rain may wash away all traces of the acid, save the corrosion ; but 
it would be under those circumstances impossible to say whether the 
corrosion was due to oxidation or a solvent. 
To sum up briefly : the characters of sulphuric acid spots on organic 
matters generally are black, brown, or red-coloured destructions of tissue, 
moisture, acid reaction (often after years), and lastly the chemical evi¬ 
dence of sulphuric acid or sulphates in excess. 
Caution necessary in judging of Spots, etc. —An important case, 
related by Maschka, shows the necessity of great caution in interpreting 
results, unless all the circumstances of a case be carefully collated. A 
live coal fell on the bed of a weakly infant, five months old. The child 
screamed, and woke the father, who was dozing by the fire ; the man, in 
terror, poured a large pot of water on the child and burning bed. The 
child died the following day. 
A post-mortem examination showed a burn on the chest of the infant 
2 inches in length. The tongue, pharynx, and gullet were all healthy ; 
in the stomach a patch of mucous membrane, about half an inch in 
