[aa] In making this experiment, if the vegetable juice be placed too near to the effervescing mixture, some particles of the acid will be forced up to it, together with the air, and may occasion an erroneous conclusion to be drawn from it. EXPERIMENT XXXVI. Twenty drops of the syrup of violets were added to a glass-full of water strongly impregnated with fixed air, after the method directed by Dr. Priestley[ab], but without any variation in the colour of the violets. [ab] Directions for impregnating water with fixed air, &c. by Joseph Priestley, L.L.D. EXPERIMENT XXXVII. A few drachms of the syrup of violets were dissolved in half a pint of water, which was afterwards impregnated with air from an effervescing mixture of chalk and the smoaking spirit of nitre; but the syrup of violets suffered no change of colour. EXPERIMENT XXXVIII. A piece of putrid flesh which had been sweetened by the vapours of iron filings and the nitrous acid, had a pungent, acidulous smell. It was carefully washed in water, and still remained free from putridity. A few drops of lixivium tartari were instilled into this water without producing any sensible effervescence. May we not infer from these experiments, that if fixed air be an acid, it is an extremely weak one, and not sufficient, as such, to sweeten putrid bodies; which effect must consequently be owing to some other mode of action, the principles of which are not as as yet positively defined? CHAP. XI. A REVIEW OF THE GENERAL CONCLUSIONS DEDUCIBLE FROM THE FOREGOING OBSERVATIONS AND EXPERIMENTS. 1. The due preparation of MAGNESIA ALBA depends on the proper mixture of the alkaline lixivium with the solution of the sal catharticus amarus; on the precipitated powder being immediately thrown into a very large quantity of boiling water; on the purity of the water used in the process; on the expeditious drying of the medicine, and on an exact attention to cleanliness. 2. The artificial Epsom salt, or _sal catharticus amarus_, affords Magnesia, at least, equally pure with that obtained from the Epsom waters; and as the writers[ac] on mineral waters mention those of Epsom to contain besides their salt, a considerable quantity of unneutralized earth, which appears, from Dr. Rutty's experiments, to be calcareous, they should seem peculiarly unfit for the purpose of preparing Magnesia. Some of the _Epsom Magnesia_ being calcined, impregnated distilled water with a calcareous earth. [ac] Allen, Lucas, Rutty, Monro, &c. 3. A sufficiently strong and well purified lixivium of potashes is equally adapted to procure the precipitation of Magnesia, as a ley made with salt of tartar, or any other fixed alkali.