Impurities. - Acid tartrate; detected by insolubility. Carbonates; by quantitative test.

Dose. - 20 to 60 gr. as a diuretic and antacid; 2 to 4 dr. as a purgative.

3. Potassae Nitras

Potassae Nitras. Nitrate of Potash, Nitre, Saltpetre. KNO3.

Source. - Found native, and purified by crystallisation. the Characters. - Striated colourless prisms, of a peculiar saline taste. Solubility, 1 in 4 of water.

Dose. - 10 to 30 gr.

From Potassae Nitras is made:

Potassae Sulphas. - Sulphate of Potash. K2SO4.

Source. - Prepared from Nitrate of Potash and Sul-phuric Acid, which yield the acid sulphate - KNO3 + H1SO4 = KHSO4 + HNO3; then adding Carbonate of Potash - 2KHSO4 + K2CO3 = 2K2SO4 + H1O + CO2

Characters. - Colourless hard six-sided pri-terminated by six-sided pyramids. Solubility, 1 in 10 of water; not soluble in spirit.

Impurities. - Other sulphates, and chlorides.

Dose. - 15 to 60 gr.

Potassae Sulphas is contained in:

Pulvis Ipecacuanha Compositus.- 8 in 10;

Pilula Colocynthidis Compositu; and Pilula Colo-cynthidis cum Hyoscyamo.

Action And Uses. 1. Immediate Local Action And Uses

Externally. - Potash, in the form of potassa caustica, is a powerful irritant and caustic, absorbing water from the part to which it is applied, and converting it into a moist, grey slough. It is used to destroy morbid growths, to form issues, and to stimulate ulcers. Solutions of liquor potassae or the carbonates neutralise caustic acids on the skin. Hot dilute solutions relieve the pains of rheumatism and gout when used as local baths or fomentations to the affected joints. Weak compounds of potash with olive oil constitute soft soaps, which also have antacid and cleansing properties.

Internally. - Potash and its salts have an alkaline action, and are employed as antidotes to the caustic acids; but the use of the carbonates for this purpose ought, if possible, to be avoided, on account of the great development of carbonic acid. In the mouth, potash checks for a moment the secretion of saliva. Reaching the stomach, it partly neutralises the contents; and liquor potassae effervescens will relieve acidity due to excess of gastric juice, or to the decomposition attending indigestion.

Of much greater importance is the stomachic action of potash given shortly before meals, when, as a dilute alkali, it is a natural stimulant to the gastric follicles, increasing the flow of the juice, and is a sedative to the nerves. Liquor potassae and bicarbonate may be used for this purpose in dyspepsia, especially when there is much pain and tendency to sickness, or when the further action of potash on the system is desired, as in gouty, rheumatic, and calculous subjects; but soda is more commonly employed. Large doses of the bicarbonate are apt to irritate the stomach.

Some valuable saline purgatives belong to the potash group, notably the acid tartrate, tartrate, and sulphate. The rationale of the action of saline purgatives is discussed in Part III. In dropsy from any cause, especially ascites from liver disease, the acid tartrate, in the form of Pulvis Jalapae Compositus, of an electuary with honey, or of a lemonade, may be used to remove the water by the bowels, its hydragogue effect being assisted by its action as a diuretic.

2. Action On The Blood And Its Uses

Potash is freely absorbed into the blood in the form of salts, and there acts both on the plasma and red corpuscles, 'increasing the natural alkalinity of the former, and improving the quality and increasing the number of the latter when judiciously combined with iron. As an alkaliniser of the plasma, although exceedingly transitory in its action, very rapidly excreted, potash is a valuable remedy in gout, where it combines with the excess of uric acid in the blood and facilitates its excretion. The carbonates, citrates, and tartrates of potash in various forms, and the waters of such spas as Baden-Baden, Wiesbaden, Vichy, Carlsbad, and Aix-la-Chapelle, which contain definite though small quantities of potassium salts, are extensively used for the treatment of acute and chronic gout. The salts of the vegetable acids, or the effervescing carbonates, are the best preparations for prolonged use. In acute rheumatism the bicarbonate, citrate, tartrate, and acetate are successfully employed to increase the alkalinity of the blood. For restoration of the red corpuscles in anaemia by the increase of their potash element, the carbonate is the best haematinic, either as contained in the Mistura Ferri Composita, or given as a pill with sulphate of iron (Blaud's Pill).

An indirect action of potash on the blood must here be carefully noted. "We shall see hereafter that citric, tartaric, and acetic acids, given internally, are partially oxydised in the blood. The completeness of the combustion, and of the important influences which the change exerts on the blood and kidneys, depends upon the combination of the vegetable acid with an alkali. Citric acid, e.g., is excreted mostly unchanged in the urine, but citrate of potash is entirely, or almost entirely, thrown out as the carbonate.

3. Specific Action And Uses

Potash depresses the muscular, nervous, and cardiac tissues; and the point of interest in this connection is, that when given for other purposes it must be used with caution. The danger of "potash poisoning" is, however, exaggerated, for the drug passes so quickly through the system, that it cannot well produce a deleterious effect on the . unless given for a very long time, or in disease of the excreting organs, especially the kidneys. Excessive single doses are generally rejected at once by vomiting.

4. Remote Local Action And Uses

Potash is excreted almost entirely by the kidneys; to a much less extent by the skin, respiratory passages, stomach, liver, biliary passages, and bowels. In other words its passes out in the fluids of all the secretory surfaces, and in doing so it stimulates the cells to increased activity.

The diuretic effect of several potash salts, referable to their influence upon the renal epithelium, is the most important of D - 8 fail; and the acetate, acid tartrate, citrate and tartrate, car-bonate, bicarbonate, and sulphate are used for this purpose in the order named. These saline diuretics are given chiefly in renal dropsy, where it is desirable to increase the functional activity of the renal epithelium, and thus the secretion both of water and urea, whilst the vessels remain undisturbed. They are also suitable diuretics in feverish conditions. In cardiac dropsy they are less beneficial, as they diminish rather than increase the force of the circulation; but in an occasional full dose they are useful adjuvants, even in this condition, to other classes of diuretics, such as digitalis and scoparium, to wash out the tubules. Nitrate of potash is a powerful diuretic, belonging partly to a different class, the local vascular stimulants. It is more suitably employed as a diuretic in feverish conditions, and to remove inflammatory effusions into the pleura and pericardium, and must be given with caution in renal disease.

As alkalinisers of the urine, the carbonate, bicarbonate, and the vegetable salts of potash are extensively used in uric acid gravel, acute and chronic gout, and acute rheumatism, the latter being preferred because less irritant. In uric acid calculus of the kidney or bladder, these salts have been successfully employed to cause actual solution of the concretions.

The diaphoretic effect of potash salts is not marked, the citrate and the nitrate alone being used for this purpose, and that only in mild feverish attacks.

The bronchial secretions may be increased and rendered less tenacious in inflammation and dry catarrh of the tubes by the potash salts, which are thus saline expectorants, the iodide in particular being useful for this purpose Gastric catarrh, especially in gouty subjects, is benefited by the milder salts of potash beyond their immediate local effect; but the mineral waters which appear to act in this way, such as those of Vals, Vichy, and Carlsbad, owe their efficiency much more to soda. The same remarks apply to catarrh of the biliary passages and tendency to gall-stones.

The action of potash on the intestinal glands constitutes it a remote as well as an immediate purgative.