By this chemical action Sulphuric Acid is rendered useful in alkalinity of the blood, which may occur in fevers; or of the urine, as in Phosphaturia. It thus acts as a Restorative Hæmatic. But it is not right that there should be more than a certain quantity of this acid in the system. So that when introduced in large quantity it must be excreted. It does not appear that it is itself excreted in the urine, though it may cause an excess of other acids in that secretion. On this point Dr. Bence Jones has made some careful experiments. (_Anim. Chem._, p. 75.) He finds that Sulphuric Acid does not pass off in the urine, either free or in combination, except when given in great quantity. Now it is found that Sulphuric Acid is of great use as an Astringent in diarrh[oe]a. Placing these two facts in juxtaposition, it would seem that the acid, which is doubtless absorbed in the first place, must afterwards be eliminated from the system by the surface of the bowels. This is perhaps because the secretion of this mucous membrane is the one which is least likely to be deranged by the presence of the acid. The free acid is an Astringent, and has the power of coagulating albumen, and causing the contraction of muscular fibre. (p. 256.) Though probably neutralized and combined while in the blood, it is free before absorption, and after excretion. Before absorption it is an Astringent to the surface of the stomach; after and during excretion, to the surface of the bowels. It is useful chemically in alkaline Pyrosis. Its astringent property explains its utility in _acid_ dyspepsia, which appears at first sight incomprehensible. Lactic acid, or some similar acid, is poured out in excess by the glands of the stomach. Sulphuric acid topically constringes the muscular fibre of the ducts of these glands, and in this way diminishes their secretion. The acid, if in excess in the blood, may tend to brace the system by causing a general contraction of the fibres of the voluntary muscles. But it is chiefly on account of its anti-dyspeptic agency, and its astringent action on the secretions, that the title of Tonic has been so often applied to it. Next to that of the bowels, the acid appears to act most on the secretion of the skin. Probably there also eliminated in a free state, it is thus able to diminish excessive diaphoresis. It is applicable in cases of Hæmorrhage, when this takes place from a mucous membrane, for it probably passes off in small quantities from all the mucous surfaces. It is very useful in diarrh[oe]a. (_Vide_ p. 294.) Being a special Astringent to the intestinal mucous surface, it may possibly be useful even in malignant cholera, especially if given in the early stage of that disorder. (_Vide_ pp. 120, 154, 262.) POTASH. Class I. Div. I. Ord. III. ALKALIA. Class I. Div. II. Ord. I. ANTIPHLOGISTICA. Class I. Div. II. Ord. III. ANTISCROFULOSA. Class IV. Ord. VI. DIURETICA.