March, 1927
INDUSTRIAL AND ENGINEERING CHEMISTRY
more, there is not and cannot be any sharp distinction between hazardous and non-hazardous oils; variations in condition of use may entirely change the relative hazards of two or more of the common commercial oils. Extreme care is necessary in obtaining significant data regarding the action of certain vegetable and animal oils which are either diluted with mineral oils or to which agents have been added which tend to retard their oxidation. For example, a mixture of 50 per cent cottonseed oil and 50 per cent asphalt-base mineral oil becomes dangerous OIL continued exposure to temperatures slightly above normal. However, when the fresh mixture is tested by any method now available
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there is no evidence of this peculiar action unless the duration of the test is considerably more than 3 hours. Consequently, tests of tendency for spontaneous heating should be made in conjunction with a reasonably critical chemical examination. It is necessary to look out for the presence of retarding agents. These agents have nearly always an affinity for oxygen and are usually soluble in water as well as in the oil. Whenever chemical examination shows the presence of reducing agents or any appreciable proportion of mineral oil in the sample, the spontaneous heating test should be continued for a longer time than usual.
A Simple and Inexpensive Kjeldahl Digestion Apparatus1s2 By E. G. Hastings, E. B. Fred, and W. H. Peterson DEPARTMENT OF AGRICULTURAL BACTERIOLOGY A N D AGRICULTURAL CHEMISTRY, UNIVERSITY OF WISCONSIN, MADISON, WIS
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LTHOUGH many types of Kjeldahl apparatus have been described,3 the writers have seen none so effective and cheap as the one described herein. The total cost of the apparatus for twelve flasks without the gas burners and rack is about fifty dollars. KO hood or suction fan is required. For two and one-half years this apparatus has been in constant use in our laboratory; during this time more than five thousand analyses have been made and it has always proved most satisfactory. The apparatus is shown in detail in Figure 1 arid in operation in Figure 2. It consists of a large lead tube 26 mm. (11/4 inches) internal diameter, with lead side arm tubes 9 mm. ("8 inch) internal diameter, and 15 cm (G inches) long carrying movable lead stoppers. These lead stoppers should be so constructed as to move freely up aiid down the
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Figure 2-One Figure 1-Cross Section of Water Injector and One Branch of Kjeldahl Digestion Apparatus
side arm tubes and thus accommodate Kjeldahl flasks with varying sizes of necks. The digestion tube is connected by a coupling t o a water injector. This consist,s of a small lead pipe passing into the larger fume tube. The end of this small pipe is closed except for the small holes as shown Received October 30, 1926, Published with the approval of the Director, Wisconsin Agricultural Experiment Station. 8 For example, S y , THIS JOURNAL, 4, 680 (1912). 1
in the figure. When the water is turned on it escapes through these holes and passes down through the fume tube, creating a suction. The flasks are joined as shown in Figure 2 and before the gas burners are lighted the water is turned on to give a slight suction. Air is thus drawn into the flasks around the loosely fitting lead stoppers and into the side arms. This current of air carries the gases produced from the flasks through the small and the large lead pipes and brings them into contact with water, which absorbs them and carries them into the drains. The writers' apparatus is designed for long-necked Kjeldah1 flasks. If short-necked flasks are used, it is necessary to change the distance of the digestion rack from the suction tubes. To secure the best results a flask should be connected to each side arm or the openings of the unused side arms closed with lead stoppers. Once digestion is well under way it is not necessary to seal all the openings. Apart from simplicity in construction and ease of manipulation this Kjeldahl digestion apparatus has other advan-
Unit of
Kjeldahl Digestion Operation
Apparatus i n
tages. It works so well that it can be installed in a genera1 laboratory, thus making it possible, to watch the progress of the digestion while other work is being done. The time of digestion is somewhat less than that required for the usual hood method. The apparatus is economical in its use of acid. Since the entire apparatus is exposed, the necks of the flasks are cooler than those under a hood and thus not so difficult to handle. The apparatus was designed and made by W.G. Huebner and M. F. Robinson of the University of Wisconsin Service Department.
