Syn. Vitriolated Tartar.


This is usually a secondary product of chemical processes, intended for the preparation of other substances. One of these is the process for procuring nitric acid from nitrate of potassa by the addition of sulphuric acid, which, in order to ensure the complete decomposition of the salt, is used in such proportion as to form a bisulphate with the potassa left behind when the nitric acid passes over. The bisulphate is converted into the sulphate, either by the addition of carbonate of potassa, or by abstracting the excess of sulphuric acid by means of lime or its carbonate, or by igniting the salt so as to decompose and drive off the excess of acid.


Sulphate of potassa crystallizes in the form of short six-sided prisms, ending in six-sided pyramids; or the two pyramids are united at their base, without the intervening prism. They are white, very hard, without smell, of a bitterish, saline, unpleasant taste, unchangeable in the air, soluble at ordinary temperatures in a proportion of water varying, according to different authorities, from 9.5 to 16 parts, considerably more soluble in boiling water, and insoluble in alcohol. They decrepitate when thrown into the fire, but contain no water of crystallization. The salt consists of one eq. of sulphuric acid and one of potassa.

Incompatibles. Sulphate of potassa is decomposed by the soluble salts of lime, baryta, silver, and lead. Tartaric acid added to its solution throws down bitartrate of potassa.

Medical Properties. Until recently, sulphate of potassa was considered as a mild and quite safe cathartic, having the general properties of the saline substances belonging to the class, with the addition of deobstruent properties in small closes, which were supposed to render it valuable in certain cases of disease. But, in the year 1843, attention was called, in the Pharmaceutical Journal and Transactions (III. 256), to its supposed possession of poisonous properties, in consequence of death having taken place, in several instances, in patients under its use. in one case, which occurred in England, two ounces were given at once, on two successive occasions, to a pregnant woman, who was seized with violent vomiting, followed by great exhaustion and death. On examination of the body, congestion of the brain was found, with hemorrhage to the amount of two ounces. it is very obvious that the salt was not, in this case, the immediate cause of death, though it may have induced the violent vomiting, and this may have led to an apoplectic seizure, by the rupture of a blood-vessel in the brain. in the same paper, other cases are referred to which had happened in France not long previously. A puerperal woman, a week after confinement, upon taking somewhat less than two drachms of the salt, was seized with vomiting and violent pains in the stomach and limbs, which recurred with increased violence at each of five succeeding doses that were taken; and death happened soon afterwards. But it is extremely doubtful how far the fatal result, in this case, was ascribable to the salt, considering the state of the woman, and the fact that she was not under medical attendance. in a third case, which appears to be well authenticated, a female who was but just over her confinement, but was in good health, wishing to repress a too abundant secretion of milk, took six hundred grains in three doses. The first dose was rejected, the second induced vomiting, purging, and cramps, and after the third she died with symptoms of cholera. After death, a portion of the salt was found undissolved in the stomach, which exhibited signs of inflammation. From the above facts, and from others which have been published, it may be concluded that, in over-doses, sulphate of potassa is capable, in certain cases, of causing irritation and possibly inflammation of the stomach, which, through the excessive vomiting and purging produced, may give rise to fatal prostration. in opposition to the immense mass of testimony in favour of the general innocence and mildness of the medicine, the facts mentioned afford no ground for ascribing poisonous properties to the salt; for even the most innocent substance, given in great excess, or under certain unfavourable circumstances, may produce the same effect.

Sulphate of potassa has been much used, in small doses, from a drachm down to fifteen grains, as a mild aperient in dyspepsia, chronic hepatic affections, hemorrhoids, etc., and has been supposed by some to possess resolvent or deobstruent properties in enlarged liver, and swollen abdominal glands in children. it has been usually given for this purpose in conjunction with rhubarb; from five to ten grains of the root being mixed with from fifteen to sixty grains of the salt. it has been supposed also to possess the property of restraining the secretion of milk; and an idea that it promotes abortion must have got abroad among the vulgar, for, in one of the fatal cases above referred to, it was given with a view to that effect. Nevertheless, I very much doubt whether it has any other powers than those which belong to the neutral alkaline salts in general.

As a mild purgative, it may be given in a dose of from three to six drachms; but care should be taken that it is dissolved. its difficult solubility is a great disadvantage; and it is highly probable that, when it has produced inflammation, the result has been owing to its exhibition in the state of powder, the hardness of the spicula of which may have proved the source of the injury.