oils and fats and a reasonable agreement with such data will generally fix the identity of the unknown oil. In making comparisons the most important figure is the iodine number because this will serve to classify the oil at once as a drying, semi-drying. or non-drying oil, the approximate ranges for these somewhat arbitrary divisions being as follows: Drying. Oils Iodine Number 200 and higher to 120 120 to 95 95 to 70 and lower The choice will, by this means, be narrowed down to a limited list of oils or fats. The remaining constants are then considered, one by one, and each comparison will narrow the choice still further. At the last all available qualitative tests are made in order to confirm the results of comparative tests or to aid in making a final decision. It sometimes happens that the figures obtained in the examination of the unknown oil will not all correspond, even to a reasonable degree, with the recorded data for any of the common oils. This may be the result of (1) errors in the determinations, (2) adulteration, or (3) a real abnormality of the oil which is being examined. The first case should be at once excluded by repeating the determination of constants in which lack of agreement is observed. A careful inspection of all data may serve to indicate certain oils which, by addition to one that most nearly resembles the oil under examination, would change the "constants" in the manner observed. The matter of commercial values should also be considered in this connection, since any commercial material is adulterated, if at all, by a cheaper material. PHYSICAL AND CHEMICAL CONSTANTS OF OILS, FATS AND WAXES-(Continued) Japan wax.. Butter.. Lard.. Beeswax. Carnauba wax. Spermaceti. Sperm oil.. Wool wax. After the decision as to the identity of the oil has been made or has been limited to two or three possible oils, consult a good reference book for a complete discussion of these oils and make any additional tests that may be there suggested. For this purpose are to be recommended the descriptive part of Lewkowitsch's Chemical Analysis of Oils, Fats and Waxes, and Allen's Commercial Organic Analysis, volume 2, part 1. The figures in the tables on pages 327 and 328 are given for the purpose of comparison. They are gathered from various published analyses of the more common oils and fats. Exact agreement should not be expected. For more extensive tables consult Lewkowitsch: Chemical Analysis of Oils, Fats and Waxes. WATER The chemical examination of water may be made to determine its fitness for drinking or for industrial uses, such as steam production, laundering, textile industries, etc. It is not necessary that a complete analysis should be made for all of these purposes because not all substances occurring in water are equally important in the different applications of the water. Natural waters often contain substances that are objectionable if they are to be used industrially and these substances are, for the most part, inorganic salts and, occasionally, acids. Most of such inorganic materials are without appreciable effect upon the human system and the examination for potability is rather directed toward the detection of pollution by sewage. On this account it becomes necessary to treat the subject of water analysis in two distinct. divisions. Industrial Analysis. By far the largest industrial consumption of water is for the production of steam and for this reason the chemist is more often called upon for the analysis of water to determine its fitness for steaming than for any other industrial purpose. Pure water, however desirable it may be for use in the steam boiler, is not a natural product. Water from streams and other surface origins contains mineral and organic substances derived from the surface soil as well as inorganic compounds derived from springs which feed the stream. Water from wells contains whatever mineral matter is common to the region through which it has flowed. Even rain water contains organic matter and ammonia and may develop organic acids when standing. Some of the compounds contained in water are comparatively unobjectionable because their action is slight. It is to be remembered, however, that in steam boilers the temperature is higher than 100° because of the increased pressure. At a pressure of 100 pounds per square inch the boiling-point of water is 164° and at 200 pounds per square inch the boiling-point is 194°. At these temperatures the chemical activity of many dissolved substances is very much augmented. According to their effects upon boiler steel the constituents of natural waters may be classified as corrosives, incrustants and foam producers. Corrosives. Any soluble compound that can dissolve iron at high temperatures will give rise to pitting of the boiler, especially when the steel is not of uniform composition. Corrosives commonly occurring in water are chlorides, nitrates, and sulphates, particularly of the alkaline earth metals, and free carbonic acid. Free inorganic acids are of rare occurrence and absolutely unfit a water for steaming without preliminary treatment. A small amount of acid will cause corrosion for an indefinite period because of the ready hydrolysis of iron salts. A cycle of reactions takes place as follows: Fe+2HCl-FeCl2+H2, 6FeCl2+30-4FeCl3+Fe2O3, FeCl3+3H20-Fe(OH)3+3HCI. A metal chloride which is easily hydrolyzed will also produce continuous corrosion: MgCl2+2H20→Mg(OH)2+2HCl, Nitrates are equally injurious, although they seldom occur in more than small concentration. Sulphates are somewhat less corrosive and free carbonic acid still less so. Incrustants. Any substance that can be precipitated by heating or evaporation of water is, in a sense, an incrustant. The steam boiler as a power producer is also a machine for continuous concentration of water solutions, since fresh, impure water is |