and perhaps the alkalies or spirit of wine mixed with it, feem to leffen its fenfibility; in order to preserve its virtues, while it is kept in a liquid state, fome fresh leaves of the cabbage, minced as has been directed, may be infufed in a mixture of vitriolic acid and water, of about the degree of acidity of vinegar; and it may be neutralized, as it is wanted, either by means of chalk, or of the fixed or volatile alkali. But it is neceffary to observe, that if the liquor has an excess of alkali, it will lofe its colour, and become yellow, from which state it cannot be reftored; therefore care should be taken to bring it very exactly to a blue, and not to let it verge towards a green.

By the fame procefs, I have made a red infufion of violets, which, on being neutralized, forms at present a very fenfible teft; but how long it will preserve its properties I have not yet determined. Probably the coloured infufions of

* Since writing the above, I have found that the infufions of red cabbages, and of various flowers, in water acidulated by means of vitriolic acid, are apt to turn mouldy in the summer seafon; and alfo, that the moulding is prevented by the addition of fpirit of wine. The quantity of fpirit which is neceffary for this purpose, I have not been able to afcertain; but I add it by little at a time, until the progress of the moulding is prevented.

other flowers may be preserved in the fame manner, by the antifceptic power of the vitriolic acid, fo as to lose little of their original fenfibility. Paper fresh stained with thefe tefts, in their neutral ftate, has fufficient fenfibility for many experiments; but the alum and glue which enter into the preparation of writing-paper, seem, in fome degree, to fix the colour; and paper which is not fized, becomes fomewhat tranfparent, when wetted, which renders small changes of colour imperceptible; fo that, where accuracy is required, the teft fhould be used in a liquid ftate *.

* I have found that the petals of the fcarlet rofe, and those of the pink-coloured lychnis, treated in this manner, afford very fenfible tefts.

XVI. On the Action of Metallic Oxides and Earths upon Oils, in low Degrees of Heat. By Mr. PETER HENRY.

From the MEMOIRS of the LITERARY and PHILOSOPHICAL SOCIETY of MANCHESTER.

THE high degree of colour poffeffed by many

of the expreffed and fatty oils rendering them unfit for feveral ufes in the arts, it appeared to be a defirable object to discover a mode of depriving them of their colouring particles.

For this purpose, the following experiments were inftituted.

1. Two ounces of fpermaceti-oil were digested with one drachm of white arfenick, in a heat of 180° of Fahrenheit, during fix hours; and left to ftand till morning. The oil was then perfectly clear and colourlefs, and much heavier than it was previous to the experiment: a great part of the arfenick, however, remained undiffolved, at the bottom of the digesting vessel.

2. Two ounces of linfeed-oil were digested with one drachm of white arfenick, under the fame circumftances with the former. In the morning,

very little alteration being perceived in the mixture, it was expofed to a fomewhat greater heat. In two hours, the oil appeared brighter and clearer, much of the arsenick being diffolved; but it yet retained a great part of its original colour. There was a confiderable depofition of mucilage; the arfenick which remained undiffolved being tinged of a light yellow colour.

3·

Green olive-oil was treated in a fimilar manner with the spermaceti-oil, and attended with the fame refult.

4. Thick train-oil was digefted with a drachm and a half of white arfenick. No great alteration was obferved in the colour of the oil, though it was evidently rendered clearer, and more limpid.

When the oils were at the greatest heat, a brisk effervefcence took place, in all of them, upon fhaking the bottles, but immediately difcontinued, on the arfenick being fuffered to fubfide. When poured on the hands, they instantly fhrivelled the fkin, and were either abforbed, or foon dried up. Two phials of N°. 1 and 2, being left expofed to the action of air and light, for fome months, were not in the least changed.

As it was evident, that a confiderable portion of arfenick was diffolved in all the foregoing experiments, I wifhed to fee if it could be precipitated, and at the fame time the oils be left pure, and deprived of colour; though with no great

hopes

hopes of fuccefs, from the known property of the mineral acids to render oils thick and difcoloured.

5. Part of No. 1 being poured into a phial, three or four drops of ftrong vitriolic acid were added. The arfenick immediately precipitated, leaving the oil as pure and colourless as before.

6. The fame quantity of vitriolic acid being added to No. 2, 3, and 4, the arfenick was in like manner precipitated. No. 2 feemed even clearer than before the addition of acid.

7. Nitrous acid being added, in the fame proportion with the vitriolic, the colour of all the oils was inftantly changed to a dark brown, except the fpermaceti-oil, which was not much affected; the train and linfeed oils fuffering the greateft change. In all of them a flight effervefcence took place.

8. Marine acid occafioned a precipitation, which foon rediffolved, in all of them.

9. Both the fixed alkalies immediately coagulated the oils; the water, in which the folution of alkali was made, fubfiding to the bottom of the veffel, along with the arfenick.

10. Three ounces of fpermaceti-oil were digefted with one drachm of litharge, during fix hours, in about 200° of Fahrenheit. The oil became much clearer than before the experiment, but not near fo colourlefs as when treated with arfenick the litharge was changed to a white colour.