Solutions of _boric acid and borax_ are frequently added to milk. Their use is objectionable (_a_) because they tend to conceal incipient decomposition, but do not prevent its possible evil effects, and (_b_) because they enable the farmer to palm off dirty milk on the public. Were the addition of preservatives to milk forbidden, the farmer could perfectly well keep his milk sweet until it reached the town-consumer by adopting strict measures of cleanliness, and by cooling his milk before it leaves the farm. At the least it should be made obligatory on the milk retailer to declare the presence of preservatives in milk sold by him. The presence of borax or boric acid can be detected by evaporating the milk to dryness, incinerating and then moistening the ash with a drop of strong sulphuric acid. If a little alcohol be now added, on applying a light, a green flame indicates boric acid. Milk or cream containing boric acid turns blue litmus paper red. _Formalin_ is also sometimes used as a preservative for milk in very weak solution. Its presence can be determined by diluting the milk with water in a test-tube, and running strong sulphuric acid down the side of the tube, taking care to prevent mixing. At the junction of the acid and diluted milk a violet ring is seen if formalin is present. _Salicylic acid_ was formerly used as a milk preservative, but is now seldom used except in beers. All these preservatives are objectionable in milk, although their injurious action may be difficult to prove. 5. =Coating with fat or gelatine= has only succeeded in conjunction with the exclusion of air. This process is especially applicable to fishes, as tinned sardines. In a modified form, it is useful in coating potted meats, etc. 6. =Heating and Air-tight Cases.=—Tinned meats prepared according to this method are imported in large quantities. In the process of preparation, the cases are packed with meat and filled up with gravy, and then closed with a cover which is hermetically sealed, except at one point. The case is then heated to 250° Fahr., in order to drive out all air, and destroy any putrefactive germs present. The open point is sealed while the gravy is still boiling, thus making the case completely air-tight. Albumin is coagulated at about 170° Fahr.; the higher temperature, which it is found necessary to employ, overcooks the meat and renders it less digestible (see also p. 40). CHAPTER VII. CONDIMENTS AND BEVERAGES.