In many cases the addition of salt in small quantity to the acid liquor will tend to deplete the hides, and at the same time prevent any injurious action of the acid. Ammonium chloride may also be used with advantage (see p. 159). A solution containing about 15 per cent. of salt and 0·3 per cent. of sulphuric acid, with some molasses, has been a good deal used in the States as a bate, and seems to answer well on some classes of goods, but the acid and salt are apt, ultimately, to find their way into the liquors and destroy tannin. The process is well suited for chrome-leather, and may also be usefully applied in cases where goods have become “wind-blasted” or otherwise impregnated with carbonate of lime, since in presence of salt the acid can be used in sufficient excess to dissolve the carbonate. Vegetable acids may, of course, be used in conjunction with salt in the same way. The salt does not neutralise the acid, but simply controls the swelling of the skin, and if acid has been used in any material excess, the first part of the tanning must be done in salted liquors, or the acid neutralised with ammonia, sodium carbonate, or chalk, previous to tanning, as, otherwise, the goods will plump up in the liquors, and be tender when tanned (cp. p. 91). Lactic acid has recently come largely into use as a deliming agent. It is best known as the acid which gives a characteristic taste to sour milk, and is the chief product of the lactic ferment. It may be very successfully used for neutralising the lime left in the skins after the depilation, but, if used in excess, it tends to plump or swell the leather very strongly, being one of the best plumping agents known. When used for deliming, a solution of 2 lbs. in 100 gallons is very suitable. It may, in many cases, be substituted for the bran-drench with advantage, and is much more rapid and less dangerous in hot weather, but the effect is not in all respects identical.[89] [89] On the manufacture of lactic acid by fermentation, see Claflin, Journ. Soc. Chem. Ind., 1897, p. 516. Campbell states that practically pure cultures of the lactic bacteria are obtained by continued culture in milk. These cultures employed as a ferment for drenches have given good results in the Yorkshire College Experimental Tannery. When lactic acid is used for bating, or drenching, the operation should always be conducted in a paddle, and the liquid works more satisfactorily if it is at a temperature of 30-35° C. As regards cost, it will be found that in practice it is not appreciably more expensive than dung or bran. About an hour’s paddling will generally suffice, if the right quantity of acid has been used, but in some cases it is best to add the acid in several portions and take more time.