The Methods of the Chemists of the United States Steel Corporation for the Sampling and Analysis of Fluxes, Cinders and Refractories, 1921, 64 pp. The Methods of the United States Steel Corporation for the Technical Sampling and Analysis of Gases, 1918, 2nd ed., 60 pp. Methods of the Chemists of the United States Steel Corporation for the Sampling and Analysis of Coal, Coke, and By-products, 1923, 184 pp. 9. The Association of Official Agricultural Chemists. Methods of Analysis. Williams and Wilkins Co., Baltimore, 1920. Chemical and Physical Tables and Data 1. The Chemists' Year Book. American Edition. The Chemical Catalog Co., New York, 1923, 1093 pp. 2. Comey, A. M. A Dictionary of Chemical Solubilities, Inorganic. The Macmillan Co., New York, 1921, 2nd ed., 1141 pp. 3. Landolt-Börnstein. Physikalisch-Chemische Tabellen. Julius Springer, Berlin, 1923, 2 vols. 4. Olsen, J. C. Van Nostrand's Chemical Annual. D. Van Nostrand Co., New York, 1922, 5th ed., 900 pp. 5. Seidell, Atherton. Solubilities of Inorganic and Organic Substances. D. Van Nostrand Co., New York, 1919, 2nd ed., 843 pp. 6. Smithsonian Physical Tables. The Smithsonian Institution, Washington, 1918, 6th ed., 355 pp. 7. Hodgman, C. D. and Lange, N. A. Handbook of Chemistry and Physics. Chemical Rubber Publishing Co., Cleveland, 1928, 13th ed., 1214 pp. 8. International Critical Tables of Numerical Data: Physics, Chemistry and Technology. McGraw-Hill Book Co., New York, 1926-1929. Volumes I to VI. Journals and Periodicals The Analyst, London, England. Journal American Chemical Society, Easton, Pa. Journal Chemical Society, London, England. Journal of Industrial & Engineering Chemistry, Easton, Pa. CHAPTER II APPARATUS. REAGENTS. DISTILLED WATER 14. Apparatus. - A detailed list of the apparatus required for a liberal outfit for a student's desk will be found at the end of the chapter. It is our purpose here to describe only the more important items which the student will use from his outfit and with respect to which a few words of explanation or caution may be necessary. Of these items he should immediately after checking over his outfit get ready the following: namely, desiccator "policeman," silver nitrate test bottle, stirring rods, and wash bottles. 15. Burners. Bunsen or Tirrill type. These burners are capable of producing temperatures up to about 800° and are useful for igniting filter papers and conducting ignitions, fusions or other operations where temperatures not in excess of 800° are required. Meker type. With this type of burner a temperature of 1300° can be reached. It is particularly useful for igniting precipitates such as silica, aluminum oxide, magnesium pyrophosphate, etc., and for conducting the fusion of refractory silicates. 16. Desiccator. A desiccator is a vessel used for the purpose of maintaining a dry atmosphere in which to place objects that might be affected by moisture or carbon dioxide. The usual type is provided with a ground-glass cover to keep it air tight, and is designed so as to provide a lower and an upper compartment. The lower compartment is kept partially filled with a suitable desiccating agent, such as concentrated sulphuric acid or anhydrous calcium chloride. While the former is slightly more efficient in that it maintains a lower partial pressure of water vapor, this efficiency is offset by the disadvantage that the acid is likely to splash around when the desiccator is being carried 1 It is assumed that the analytical balance which is required by the student will be furnished apart from the outfit for his desk. about. This splashing can be obviated somewhat by filling the lower part of the desiccator with glass beads. When anhydrous calcium chloride is used it should be granular and free from dust, and should be renewed occasionally. The upper compartment is fitted up particularly for the accommodation of crucibles. For small desiccators, which as a rule will take only one crucible, the fitting up is accomplished very satisfactorily by taking a silica or clay triangle with wire ends, and bending the ends so that they are perpendicular to the plane of the triangle, and then spreading them sufficiently so that their feet will press against the walls and floor of the compartment, thus preventing the triangle from sliding around. If the ends are too long they can be cut off or bent back on themselves. Triangles of metal should never be used unless constructed of platinum. The ground-glass portions of the desiccator should be greased with a little vaseline so as to make the desiccator air-tight. Caution in Use of Desiccator. When a hot object is placed in a desiccator a sufficient time should elapse for the air to become heated and expanded before putting the cover in place, say 5-10 seconds; and in removing the cover it should be slid open very gradually so as to prevent any sudden inrush of air due to the partial vacuum which exists in the desiccator as a result of the previous escapement of hot air when the heated crucible was put in the desiccator. Failure to observe these precautions will often result in some of the precipitate being blown out of the crucible. 17. Hydrogen Sulphide Generator. It is customary now to make hydrogen sulphide precipitations under slight pressure in a rubber-stoppered flask, preferably an Erlenmeyer flask, rather than to allow the hydrogen sulphide to escape into the air from an open beaker or one covered with a watch-glass. As for the matter of the slight pressure which is necessary, any form of Kipp generator is suitable; hence it is mostly a question as to the propersized generator to select in order that the capacity be sufficient for the demands upon it. For a general routine laboratory it is advisable to have a fairly large-sized generator always ready for service, but for student work it has been found more satisfactory to provide each student with his own small outfit which he gets ready as wanted. For the student's individual use the generator devised by Mr. Reginald M. Banks has answered admirably. The general assembly of the Banks generator is shown herewith: Directions for Use. The generator is connected with an empty flask which is to serve as a trap in case any of the solution comes over from the generator; the safety flask is connected with the flask which contains the solution to be saturated with hydrogen sulphide; at 14 it is advisable to place a small plug of cotton wool as this substance will mordant out any ferrous chloride that has been carried along with the hydrogen sulphide gas stream by entrainment. The hard rubber screw clamp 8b is opened and hydrogen sulphide allowed to displace the air in the safety flask and in the precipitating flask. The screw clamp is then closed and air pumped into the generator until a slight pressure is indicated; one or two squeezings of the bulb are generally sufficient. No further attention is required until the precipitation is completed. This completion may be ascertained by giving the precipitating flask a gentle shake. If the pressure as indicated by the manometer does not show a momentary drop, the precipitation is complete. When this has happened, close the screw clamp 8a, disconnect the safety flask, and the generator may be put aside until needed again. The rate of precipitation is often materially accelerated by giving the precipitating flask a gentle rotary motion every now and then. The following precautions should be observed. When the generator is under pressure, the screw clamp 8b must not be opened nor the precipitating flask disconnected, without first closing the screw clamp 8a. The stoppers in the flask and generator must be securely inserted. The screw clamp 8 must be closed after pumping the necessary air into the generator, and after precipitation is complete and the flask disconnected, it should be opened again before connecting the generator up for a precipitation. The opening of this screw clamp allows the pressure to return to atmospheric in the generator. 18. The Jones Reductor. This is a cylindrical tube of about 2 cm. internal diameter and 40 cm. length, enlarged at its top end so as to form a reservoir of about 100 c.c. capacity and drawn out at its bottom end into a smaller tube of about 0.5 cm. diameter and 30 cm. length. The preparation and use of the Jones reductor can best be postponed until we come to the subject of oxidationreduction (see § 272). 19. Platinum Crucibles. Use and Care. Platinum crucibles should have a capacity of about 25 c.c. for ordinary routine work and should be supplied with a cover. In using platinum crucibles certain precautions should always be observed, as platinum is very easily damaged. It must be handled with mechanical care, as otherwise it will soon become dented and distorted on account of its softness. With respect to its chemical behavior it must be remembered that platinum is attacked even at ordinary room temperatures by strong oxidizing agents, such as nitrohydrochloric acid (aqua regia), free chlorine and bromine, and at somewhat higher temperatures by ferric chloride. It forms brittle compounds or alloys with free sulphur, phosphorus, arsenic, selenium, etc., and with low melting alloys, and also with metals which are easily reduced, particularly mercury, lead, bismuth, tin, antimony, etc. Hence these elements or their compounds should never be heated or fused in platinum. With respect to strong alkalies, the hydroxides of potassium, sodium, lithium and barium must not be fused in platinum; the use of silver or nickel crucibles is recommended for such fusions. However, the carbonates of the strong alkalies may be fused in platinum. In heating platinum crucibles over a gas flame they must be kept out of the reducing zone of the flame, because contact with the hot unburned gases of this zone produces a gray crystallization on the surface of the platinum, and this effect, if not removed by gentle rubbing with a suitable abrasive, will soon spread throughout the crucible and ultimately bring about cracks in it. While being heated the crucible should be supported upon |