In practice the best effects are obtained if the raw materials treated are in a finely-divided state. therefore the tartar and the chalk should be previously finely ground. Rather more than is absolutely necessary of the carbonate of lime should be employed, and it may be replaced by other suitable carbonates.
A low degree of pressure is sufficient for carrying out the operation, but a higher pressure should be employed in order that the work may go on more rapidly. High pressure hastens the reaction, The pressure may be regulated by the volume of the vessels employed. lf, for instance, in a vessel of about 1000 gallons capacity are treated 1881 bitartrate of potash.
1000 carbonate of lime.
5720 water.
8601 After the operation are obtained 2600 crystallized tartrate of lime.
1001 bicarbonate of potash} .
solution 1 : 5.
5000 water 8601 In consequence, it is preferable to conduct the operation in the smallest possible space in order to obtain a pressure as high as possible. As mixing vessels, the well-known apparatus used in the manufacture of aerated ,waters can be employed, with the modification that the openiuga for filling in the substances and for getting out the mixture must be wider, and the stirring apparatus must be of greater strength. The apparatus is provided with a pressure gauge and safety valve, aod is connected with a conduit pipe for carbonic acid. The substances are rapidly filled in, the appazatus closed, the stirrer moved, and the operation may be observed by means of the pressure gauge, When all pressure has disappeared, carbonic acid is to be pumped in. As by the mixture and the filling in of the matters a small quantity of carbonic acid is lost, and also neutral tartrates (generated by the decomposition) may be present in the raw material, and as the reaction can only be terminated if there be a sufficient quantity of carbonic acid for converting the whole quantity of potash into bicarbonate, this addition of carbonic acid is indispensable. In consequence car bonic acid is pumped in -until the pressure in the apparatus has become constant, and no carbonic acid is confined. It is not necessary to defer pumping in carbonic acid until all pressure has disappeared, but the pumping in can be begun if the indicator of the pressure gauge continues to fall. The addition of carbonic acid is stopped when the pressure has become constant, at which moment the operation is terrninated. The freely developed carbonic acid is blown off, or the pres
sure of the same is used for transferring the contents of the vessel to other rooms, The apparatus is emptied and the mixture separated in any known manner. A precipitate of tartrate of lime and a solution of bicarbonate of potash are obtained. The precipitate is washed, and then trans ferred for the manufacture of taztaric acid. The washing water still contains a certain quantity of bicarbonate of patassa, and in order that this carbonate may also be obtained, this water is used in a further operation in lieu of pure water. The solution of bicarbonate of potash is evaporated in the ordinary way.
The small quantity of carbonic acid wanted for the work is to be borne in mind during the evaporation of the leys of carbonate, As for every atom of tartar one atom of carbonic acid is developed, the greater part of this gas remains for any desired use. Upon the same principle neutral tartrates of alkali may be deconiposed, and the mother leys of the manufacture may be used.
Neutral tartrate, together with carbonate of lime and carbonic acid under pressure, furnishes tartrate of lime and bicarhonate. In this case the whole intermediate carbonic acid is of course taken from outside, and the operation must take place under a strong pressure of from 5 to 10 atmospheres, more or less, if the decomposition is to be terminate,d within a suitable time. Without such pressure the decomposition of the neutral tartrates eannot be effected.
Messrs. Jouette and Pontieves have endeavoured to make tartaric acid from the pressed out or distilled grape skins which at present have a value only as manure. They proceed as follows :— The skins are mixed with 2 per cent. of sulphuric acid and boiled for several hours. The tartaric acid present is then liberated, while the unfermented part of the sugar, as well as the appreciable quantity that may be formed by the action of the sulphuric acid on the cellulose residue after, undergoing fermentation and subsequent distillation, will yield a not inconsiderable amount of alcohol. After decanting the sugary fluid, milk of lime is added, forming a tartrate of lime, from which the tartaric acid can be recovered in the usual way. According to these investigators, the residue from making 22 million gallons of wine, when treated as above, will yield nearly 200 tons of tartaric acid, worth about 24,000/.