IXDUSTRIAL AND ENGIA'EERIXG CHEMISTRY
December, 1926
produces a marked effect, but the addition of noncarbonate magnesium, calcium, and potassium salts increases this effect. No experiments were made to determine the effect of increasing the concentration of bicarbonate alone. High initial hydrogen-ion concentration decreases the biochemical oxygen demand, but moderately low hydrogen-ion concentration seems to be without effect. These results are of considerable importance when it is considered that the biochemical oxygen demand test is being used in various laboratories and that the results of the various laboratories are being compared. Up to 5 dags the results using distilled water for dilution are quite similar to those to which inorganic salts have been added; if differing a t all they are slightly lower. For longer periods of' incubation dilution water containing added salts gives distinctly higher results than those with distilled water alone. The second stage of deoxygenation is apparently eliminated when distilled water is used for dilution purposes. It is, therefore, doubtful that the results from various laboratories will be comparable if simply tap water is specified, because the mineral contents of different tap waters differ considerably. I n the case of trade wastes containing acid or alkaline substances the adjustment of the initial pH is very important. If this test is to be used as a standard test to determine the strength of sewage and the results from one laboratory are to be compared to those from another, it would be advisable that further work be done along these lines with the view of developing a standard dilution water which could be duplicated in various laboratories. The present specifications for dilution water given in Standard Methods of JT:iter Analysis cannot well be met in many laboratories, because dilution water is specified which shall not contain more than a specific maximum of iron or nitrogenous compounds. I n many laboratories such tap water is not available, and if the test is run with tap water of different salt concentrations the total biochemical oxygen demands of sewages of similar strength may be found t o be quite different in the various laboratories because of the effect of inorganic salts.
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Conclusions
It is desirable that a standard dilution water for biochemical oxygen demand tests of sewage be developed which would give comparable results and which could be duplicated in various laboratories. The present specifications for dilution water given in Standard Methods of Water Analysis of the American Public Health Association cannot be met in many laboratories, and these specifications do not take into consideration the effects of the different inorganic salt concentrations of different waters now used as diluents in various laboratories. Addition of inorganic salts to the dilution water used in the deoxygenation experiments produced two-stage deoxygenation curves. (Dilute sewage made up with distilled water, without the addition of such salts, uniformly gave single-stage curves.) The second stage seems to be primarily nitrification. The total biochemical oxygen demand is increased by increasing the concentration of inorganic salts. Especially for longer periods of incubation is this noticeable, even when the mineralization reached would be considered moderate or high. The bicarbonate salts alone, while producing a marked effect, do not produce so great an effect as with the addition of magnesium, calcium, and potassium salts. That the lag phase in the rate of deoxygenation of diluted sewage a t low temperatures is due to the lack of a sufficient number of low-temperature tolerant organisms capable of carrying on the deoxygenation a t a normal rate has been confirmed. Cultural studies on bacteria isolated from sewage dilutions incubated a t low temperatures show a preponderance of rod forms, a large percentage of chromogens, and a large percentage of organisms capable of carrying on proteolytic reactions. The killing of plankton by heat does not in all cases prevent the production of two-stage curves for deoxygenation of polluted stream water. Intense heat seems to decrease the total biochemical oxygen demand of such polluted stream water. (This effect was not obtained to the same degree in all experiments.)
~
Lubricants for Ground-Glass Joints' By M. J. Bradley and H. E. Wilson L'NIVERSITY OF ILLISOIS, URBAKA, ILL.
T
HE ideal lubricant, one suitable for all the various conditions under which ground-glass joints are used, is not a commercial commodity. There are two or three mixtures obtainable under the trade name of "stopcock grease" which are fairly satisfactory for pressure or vacuum joints but they are readily attacked by strong chemical reagents. During an investigation on decomposition processes of certain products of coal carbonization,2 it was found that the usual lubricants were destroyed by the strong chemical reagents used as absorption solutions in the Orsat gas apparatus. After considerable experimentation several lubricants were compounded which were satisfactory not only on the Orsat machine but also on ordinary stopcocks with gas under 10 inches of water pressure and also a t reduced pressures down to 5 or 6 mm., and also on a yacuiim desiccator !id. Heavy liquid paraffin oil (Stanolind) was found t o be much superior to petroleum jelly as a base material 1 2
Received April 8, 1926. Bradley and Parr, Chem. M e t . Eng
, 27, 737 (1922).
in the lubricants. The texture of the semisolid lubricant was greatly improved by vigorous stirring while heating on the steam bath and also by incorporating on a glass slab after congealing. Inert Lubricants
The following mixture was found to be exceedingly stable and otherwise satisfactory in contact with 40 per cent potassium hydroxide solution, saturated bromine water, fuming sulfuric acid, and potassium pyrogallate: (1) Heavy liquid paraffin oil (Stanolind) and Parowax ( 5 :6). Melt the Parowax over a steam bath and take into solution in low-boiling petroleum ether, add the paraffin oil, and heat the mixture on the steam bath with constant stirring until the solvent is removed. The smoothness and body of the lubricant can be materially changed by varying the proportions of the constituents or leaving a small trace of solvent in the mixture. The Parowax may be replaced by ceresin, giving a somewhat more greasy lubricant but one slightly less stable in the presence of fuming sulfuric acid.
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INDUSTRIAL A N D ENGINEERING CHEMISTRY
Vol. 18, No. 12
Pressure Lubricants
Special Lubricants
The following lubricants have good adhesive properties, but do not stand up quite so well in contact with strong chemical reagents. However, they are much more stable than the vaseline mixtures generally used.
Where the joints are not subjected to changes in pressure varying greatly from atmospheric, special materials may often be used with a fair degree of success.
(1) Parowax, heavy paraffin oil, latex crepe (2:5:1). Melt the Parowax on the steam bath and add the paraffin oil and latex crepe. Continue t o stir and heat until all the solvent has been removed. The Parowax may be replaced with beeswax, ceresin, or lanolin if a heavier body is desirable. _- ( 2 ) Heavy paraffin oil and latex crepe (3:4). Heat the paraffin oil and latex crepe with rapid stirring on a steam bath until the solvent is all removed. This gives a semifluid lubricant which stands up exceptionally well under heavy pressure. ( 3 ) Beeswax and lanolin (1:2). Melt on a steam bath with constant stirring. (4) Heavy paraffin oil and beeswax (1:l). Melt on the steam bath with thorough mixing until the mixture becomes chilled.
The latex crepe should be dissolved in a mixture of petroleum ether and benzene to form a heavy, viscous liquid before adding to the other constituents. This method gives a clear, homogeneous product without discoloration due to charring which takes place when the solid latex is heated high enough to melt.
(1) Fuming sulfuric (20 per cent SOs) or sirupy phosphoric acid, or even phosphorus pentoxide, may be used t o withstand bromine vapors or acid fumes. However, they lack body and are difficult to apply satisfactorily. ( 2 ) Blackstrap molasses or glycerol may be used where oils, fats, waxes, and rubber may be objectionable-for example, where kerosene is used for dilatometer determinations. ( 3 ) Ordinary petroleum jelly may be used in special cases, but it lacks body and is readily attacked by strong chemical reagents. (4) Deflocculated graphite thoroughly ground with heavy paraffin oil makes a n exceptionally good lubricant for metal joints.
Application
The old lubricant should be entirely removed and in most instances it is preferable to wash the surfaces with a volatile solvent such as ether before applying new lubricant, As a general rule, the smaller the quantity, so long as the film is entirely continuous, the better the results. A thin coating on one surface is sufficient and is usually more evenly applied with the fingers.
Properties of Some Sand-cast Aluminum-Magnesium Silicide Alloys' By Samuel Daniels WAR D E P A R T M E N T , AIR SERVICE, MCCOOK FIELD,DAYTOS,OHIO
The magnesium silicide alloys do not possess valuable the quenching temperature. 2 AGNESIU&I silicide, Mg&3i, takes a place properties in the sand-cast condition, but when The increase in strength and beside the compound quenched and artificially aged those quasi binary alhardness conferred by such loys which contain from about 1.25 to 1.75 per cent of n a t u r a l aging may be enC u A l z i n i t s a b i l i t y prof o u n d l y to affect the methis compound develop an excellent combination of hanced by artificial or acstrength and ductility. The benefits to be derived from celerated aging a t (elevated) chanical properties of alumithe heat treatment of alloys of this composition are temperatures between 100" num alloys, especially after heat treatment. Hanson and to be utilized rather in the wrought materials, of which and 200" C., but with attendthe proprietary 51s alloy is an example. The metalant decrease, as in natural Gaylerz established the equilography of the series is described and illustrated. aging, of the percentage of l i b r i u m diagram shorn in Figure 1, which m a n i f e s t s el~ngation.~~~ that the Al-?rlgpSi alloys form a quasi binary system, Archer and Jeffries4 have described the attributes of the wherein a maximum of 1.6 per cent of MgzSi (I per cent proprietary 51s wrought aluminum alloy, which, containing magnesium, 0.6 per cent silicon) is soluble a t the eutectic 1 per cent each of magnesium and silicon, represents the temperature, 580" C. With decrease in temperature the commercial application of the principles just enunciated. solubility falls, along the line NN,, to not more than 0.5 They state that this alloy differs from a purely silicide per cent of MgzSi a t 30" C. Magnesium in excess of that material in that the silicon content is deliberately in excess amount necessary to form Mg2Si causes rapid diminution of of the theoretical 1.75 Mg : 1Si (Mg2Si) ratio in order to the solubility a t high temperatures; and excess of silicon was compensate for the fact that iron, present as an impurity, reported to exert only little effect upon solubility conditions. may unite with some of the silicon and render it unavailWhen MgzSi has been dissolved and retained in the alu- able for magnesium silicide formation. The properties of minum-rich solid solution by quenching, the alloy is subject 515, depending upon its condition of treatment, embrace a to age-hardening, a process involving the reprecipitation, range in ultimate strength of from 14,000 to 50,000 pounds from the supersaturated solution, of MgzSi in highly dispersed per square inch, in elongation of from 30 to 10 per cent, particles, and adding further increment to the strength and and in Brinell hardness of from 15 to 100. It is the lighthardness, which have already been improved by the quenching. est of the high-strength alloys, having a specific gravity of Hanson and Gayler, working with wrought materials, were 2.69. The present paper is the fourth of a series of investigations' the discoverers of age-hardening caused by reprecipitation of MgzSi, and they pointed out that quenched aluminum- into the properties of sand-cast alloys of the aluminumMg& alloys age-harden a t atmospheric temperature, to an :Institute Mechanical Engineers, 11th Report t o Alloys Research extent dependent upon the quantity of MgzSi in solution a t Committee, 19p1, p. 241,
M
Published by permission of the Chief of 1 Received May 27, 1926. Air Service, w a r Department. f J. Inst M e l d s , 36, 321 (1921)
4
I
Archer and Jeffries, Trans. Am. Inst. Min. Met. Eng ,71, 828 (1925). Daniels, T ~ 1 3JOURNAL, 16, 1243 (1921); 17, 486 (1925): 18, 393
11926).
