Hence, in practice, for every ten parts of chrome alum 2.86 parts of soda crystals (or 1.06 parts anhydrous soda) are used. A convenient "stock solution" is of 10 per cent. strength. Thus 10 lbs. of chrome alum is dissolved, made basic, and made up to 10 gallons. To dissolve the alum a mechanical stirrer is necessary, for the water must not be more than warm. The disadvantage of this liquor is the limited solubility of chrome alum and the need for its solution in the cold. Liquors may be also made by dissolving chromium hydrate in hydrochloric acid, and making basic to correspond to the formula Cr{2}(OH){3}Cl{3}. Many preparations are on the market containing both chlorides and sulphates with appropriate basicity. Chrome alum liquors have been less often used in Britain of recent years owing to the high price of chrome alum, caused in part by the presence in the salt of potassium, all the salts of which have been scarce and dear under war conditions. Of the second type Procter's "glucose liquor" is a good example. Use 5 lbs. sulphuric acid, 6 lbs. sodium dichromate, and 7 lbs. of glucose, or quantities in similar proportion. The dichromate is first dissolved, and the acid added gradually. The glucose is then added cautiously on account of the brisk effervescence of carbon dioxide. A glucose of good quality is necessary, and the proportion to be used is not quite definite, for sufficient only is needed to effect the reduction, and this amount is influenced by the rate of addition and temperature of the mixture. The reduction should be careful and regular, or the oxidation products will be irregular and have a varying effect upon the tanning. Molasses can be substituted for glucose, in amounts varying with its strength. Of the third type the most common is that in which the dichromate is reduced by sulphuric acid and sodium bisulphite. Solid bisulphite may be used, but it is usually dear, and solutions are more commonly employed. Into this type fall also the liquors formed by passing sulphur dioxide gas into dichromate solution. Stock liquors of this type have the advantage that strong solutions may be made (up to 18 per cent. Cr{2}O{3}); they have the disadvantage that they are liable to contain excess of free sulphurous acid. The method of application of chrome liquors is usually by paddling or drumming the goods in solutions of appropriate strength--broadly speaking, paddles used for lighter goods and plain finishes, and slowly revolving drums for heavier hides and grained finishes. Heavy chrome leather is often tanned in pits by suspension just as in vegetable tanning. In such instances rockers may be usefully employed.