SALICYLIC ACID (This is not often used as a preservative of milk.) _Leach suggests the following method for its detection._--Dissolve one gram of mercury in 2 grams of nitric acid (sp. gr. 1.42) and then add to the solution the same volume of water. Add 1 cc. of this reagent to 50 cc. of the milk to be tested, and shake and filter. The perfectly clear filtrate is shaken with ether and the ether extract evaporated to dryness. Then add a drop of ferric chlorid solution, and a violet color will be produced if salicylic acid is present. BUTTER Butter is often colored with annatto, saffron, turmeric, marigold or coal-tar colors. By a certain process, stale or old butter is sometimes worked over and made to appear fresh for a time. This is sold under the name of “process” or “renovated” butter. Foreign fats like cottonseed oil, sesame oil, or oleomargarine may be substituted for or added to pure butter. COLORING MATTER _Martin’s Test._--Add 2 parts of carbon bisulfid, a little at a time and with frequent shaking, to 15 parts of alcohol. Shake 25 cc. of this solution with 5 grams of the butter, and let stand for some time. The carbon bisulfid dissolves out the fatty matter and settles to the bottom. The alcohol remains on top and will dissolve out any artificial colors that may be present. If only a little coloring matter is present use more of the butter. ANNATTO Evaporate a portion of the extract to dryness and add sulfuric acid to the residue. If annatto is present a greenish-blue color forms. Should a pink tint result the presence of a coal-tar color is to be suspected. COAL-TAR COLORS These colors will dye wool or silk if pieces of the fiber are boiled in the diluted alcoholic extract, which has first been acidified with hydrochloric acid. The normal butter coloring matter will not dissolve when thus treated. _Geisler’s Method._--To a few drops of the clarified fat on a porcelain surface, add a very little fullers’ earth. If a pink to violet-red coloration is produced in a short time the presence of an azo-color is indicated. SAFFRON When saffron is present, nitric acid colors the alcoholic extract green, and hydrochloric acid colors it red. TURMERIC Add ammonia to the alcoholic extract, and if it turns brown it indicates the presence of turmeric. MARIGOLD Add silver nitrate to the extract, and if it turns black the presence of marigold is indicated. PROCESS OR RENOVATED BUTTER Heat a little of the suspected butter in a spoon or dish, and if it is process butter it will sputter, but not foam much. Make the test also with some butter known to be pure and fresh.