SULPHUROUS ACID.
269
Characteristics. —This acid is readily known by its peculiar odour(that of burning sulphur). If the puce-coloured or binoxide of lead beadded to it, the white protosulphate of lead is formed. An aqueoussolution of this acid, mixed with iodic acid, deoxidizes the latter, andsets iodine free, which may be recognized by its producing a blue colourwith starch. The sulphates evolve sulphurous acid by the action ofstrong sulphuric acid.
Composition. —If 16 parts (by weight)of sulphur be burned in one volume or16 parts (by weight) of oxygen gas, weobtain one volume or 32 parts (byweight) of sulphurous acid gas.
The composition of this substance may, therefore, be thus expressed:—
CONSTITUENTS.
RESULTING
COMPOUND.
Oxygen
and1 eq.
Sulphur == 16.
Sulphur. 1 .... 16 .... 50 .... 49*968
Oxygen. 2 .... 16 .... 50 .... 50*032
Sulphurous Acid. ... 1 .... 32 .... 100 .... 100*000
Physiological Effects, (a.) On vegetables. —It is a most powerfulpoison to plants even in very minute quantities (Christison, On Poisons,3d ed. p. 750).
(b.) On animals generally. —The effects on animals have not beenexamined: but they are probably those of an irritant and an asphyxiat-ing agent.
(c.) On man. —Applied to the skin this acid gas causes heat, pain, anditching. If an attempt be made to inhale it in the pure state, it excitesspasm of the glottis. Diluted with air it may be taken into the lungs,and there acts as a local irritant, causing cough, heat, and pain.
Uses. —It has been used as a disinfectant, as a remedy for the cure ofitch, and as a nasal stimulant in syncope.
As a disinfectant it is mentioned by Homer. The mode of using it forthis purpose is very simple. A pot containing burning sulphur is intro-duced into the room or place to be fumigated, and the doors and windowscarefully closed.
As a remedy for itch, baths of sulphurous acid gas are mentioned byGlauber in 1659. They are commonly termed sulphur baths, and maybe had at most of the bathing establishments of the principal towns ofthis country. At the Hopital St. Louis, in Paris , a very complete appa-ratus for the application of this remedy in diseases of the skin has beenerected by D’Arcet. It is a kind of box, inclosing the whole body, withthe exception of the head. The sulphur is placed on a heated plate inthe lower part of the box. From ten to tw enty baths, or even more, arerequisite for the cure of itch. “ Sulphureous fumigations,” says Rayer{Treatise on Diseases of the Skin, by Dr. Willis, p. 347), “ which areemployed in some hospitals, are not attended with expense, leave nounpleasant smell, and do not soil the linen ; but the long continuance ofthe treatment necessary to relieve the disease, more than counterbalancesthese generally insignificant recommendations.” There are various otherdiseases of the skin in which baths of sulphurous acid have been foundmore or less successful, such as chronic eczema, lepra, psoriasis, impe-tigo, and pityriasis. (For further information on this subject, consult