ated to dryness, and the residue ignited. If the ignited mass be now acted on by water, and the resulting solution filtered, it will contain an amount of carbonate of potash equivalent to the quantity of tartrate of potash originally existing in the wine, for during ignition, the tartrate of potash is decomposed with the formation of carbonate of potash. A little more carbonate of potash will, however, be formed than is entirely due to the quantity of tartrate originally existing; for the other organic acids in the wine, as acetic, &c., also furnish a little carbonate of potash, but the quantity is so small it may be safely neglected. If the solution of carbonate of potash, so obtained, have a dilute sulphuric acid of known strength added to it, so long as it continues to be alkaline to test paper, and the amount of sulphuric acid so employed be noted, the quantity of bitartrate of potash originally present in the wine can be readily determined; for 40 parts of dry sulphuric acid correspond to about 188 parts of bitartrate of potash. As the author will have hereafter to advert to the determination of the quantity of alkali existing in a solution, he will fully describe the preparation of a test acid, of a known strength; the apparatus to be employed (Schuster's Alkalimeter), and mode of use having already been pointed out at page 97. The test acid is thus prepared. Take a pint or so of water, and add to it one fourth its weight of the concentrated sulphuric acid of the shops. Care must be taken to mix the liquids gradually, and in an earthenware vessel, because if mixed suddenly, and in glass, the temperature would be so rapidly augmented as to occasion a fracture of the vessel, and consequent loss of material. After mixture, it must be allowed to cool, and if not quite bright, filtered. The specific quantity must now be taken as explained (page 95), and reference had to the table in the appendix to ascertain the per centage of dry acid the liquid contains; when this is known, the analysis can be proceeded with. Determination of the amount of sulphuric acid in Wine. This may be effected by evaporating a pint of wine to about one fifth the original volume, then adding an excess of solution of chloride of barium, together with as much hydrochloric acid as will render the whole considerably acid. The precipitate of sulphate of baryta which falls is to be collected on a filter, washed, dried, ignited, and weighed, every 116 parts correspond to 40 of sulphuric acid. Estimation of Lime. A pint of the wine is to be evaporated to one-fifth its original volume, and an excess of solution of oxalate of ammonia added. The precipitate of oxalate of lime which is thus produced, is to be collected on a filter, washed, dried, ignited, treated with strong sulphuric acid, and the resulting sulphate ignited and weighed, every 68 parts correspond to 28 of lime. Or the oxalate produced as above may be ignited at a gentle red heat, and allowed to cool, a few drops of solution of carbonate of ammonia are added, and the whole evaporated to dryness, and gently heated to drive off the excess of carbonate of ammonia, every 50 parts of the resulting carbonate of lime correspond to 28 parts of lime. |