I N D U S T R I A L A N D ENGINEERING CHEMISTRY
August, 1926
have the same resistance to breaking stress as lubricants made from California oil or other highly asphaltic base oils. It therefore seemed worth while to examine some of the oils described in these papers as to their behavior in lubrication. The observations in Table VI11 were made on a hard babbitt bearing, twelve years in use in this work, kept a t an exact standard by an oil with frictional coefficient 0.0044, temperature 80-90' C., under 3000 to 6000 pounds pressure, no smoke and no break a t 6000 pounds. No lubricant should show smoke under 5000 pounds and should not break under 5500 pounds. Under these conditions, and with suitable regulation of speed, the results of such oil tests are as reliable as any other tests controlled by a proper standard.
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Acknowledgment
The writer desires to express his obligations to the Texas Company, the Sinclair Refining Company, the National Refining Company, the Indian Oil Company, the Ohio Valley Oil Company, the Fred G. Clark Company, the Pure Oil Company, the Sterling Oil Company, the Sun Oil Company, and especially to Orton C. Dunn of Smith & Dunn, Marietta, Ohio, for generous supplies of crude oils and lubricants, to W. H. Parish, and to K. G. Mackenzie of the Texas Company for valuable suggestions in the progress of this work, and to his assistants, N. Marmelstein and A. S. Gressel, for efficient aid.
The Determination of Biguanide' By C. D. Garby FIXEDNITROGEN RESEARCHLABORATORY, WASHINGTON, D. C.
IGUANIDE is one of the numerous compounds that can be indirectly derived from cyanamide. A great many of its derivatives have been prepared, but little attention has been given to a quantitative method for its determination. It has usually been estimated as the copper salt precipitation from an alkaline solution, but no specific directions have been given for this determination. In order to distinguish between biguanide and closely related compounds, the method described herein has been developed in this laboratory. A few of the properties of biguanide compounds that are of interest in this determination will be mentioned. Biguanide salts, such as the nitrates or hydrochlorides, form precipitates with copper or nickel salts when the solutions are made alkaline with ammonium hydroxide in the presence of mannite. Two distinct forms of crystals are produced, such as nickel biguanide nitrate, Ni(C2NaH&.2HN03 (needles), and nibkel biguanide hydrate, Ni(C2N&H&.2Hz0 (plates). The nitrate is precipitated in slightly alkaline solutions, while the hydrate is precipitated in strongly alkaline solutions. This compound has many of the properties desirable for the determination of biguanide by a gravimetric method. It is insoluble in alkaline solutions, comparatively stable a t 120-125' C., has a fairly large molecular weight, and is readily filtered from the mother liquor. The method as given ii a modification of that used for the determination of dicyanodiamide as nickel guanylurea.* The conditions given for the precipitation of nickel guanylurea hydrate are conditions which will also quantitatively precipitate nickel biguanide hydrate. The problem therefore resolved itself into finding the conditions under which biguanide salts would precipitate with nickel while the salts of guanylurea would remain in solution. Advantage was taken of the solubility of nickel guanylurea in strongly ammoniacal solutions; the control of the alkalinity by means of a suitable indicator; and the time required for the precipitation of nickel guanylurea hydrate when these conditions were strictly adhered to.
B
Reagents
The reagents required for the nickel biguanide determination are as follows: (1)0.12 per cent ammonia water (5 cc. concentrated NH40H per liter) ; (2) mannite; (3) diammonium hydrogen phosphate; 1 2
Received June 8, 1926. THIS JOURNAL,17, 266 (1925).
(4)nickel reagent (40 grams NiNOa. 6H20, 100 cc. 10 per cent mannite, water solution, 40 cc. concentrated N&OH, 15 cc. 25 per cent KOH); (5) 25 per cent potassium hydroxide; (6) concentrated ammonium hydroxide; (7) trinitrobenzene, saturated alcoholic solutions. Procedure (a) I n absence of guunylurea. Make up a sample of convenient size, containing approximately 0.1 gram of biguanide salt, to a volume of 25 to 30 cc. in a large-mouthed, glassstoppered weighing bottle or other suitable glass-stoppered container. To this solution add sufficient mannite to make an approximately 10 per cent solution, 10 cc. of concentrated ammonia, 5 drops of trinitrobenzene, and drop by drop sufficient 25 per cent potassium hydroxide to produce a color change from dark red to yellowish red. (An excess of KOH in the absence of guanylurea produces no bad results.) Then add from 0.5 to 3 cc. of nickel reagent, depending upon the amount of biguanide present. Allow the stoppered samples to stand for from 2 to 3 hours and filter through a weighed Gooch crucible. Wash with 100 cc. of solution (1). Dry at 125' C. for 1 hour to remove water of crystallization. Weigh as nickel biguanide Ni(C2N5H&. (6) I n presence of guanylurea. Make the sample up to 30 cc. as directed in (a). Add sufficient mannite to make a 10 per cent solution (2.5 grams), 0.2 gram diammonium hydrogen phosphate; 0.1 gram ammonium nitrate, provided no ammonium salts are in the sample, 10 cc. of concentrated ammonium hydroxide, 5 drops indicator, and drop by drop sufficient 25 per cent potassium hydroxide to produce a color change from cherry-red to reddish yellow. Add from 0.5 to 3 cc. of nickel reagent, allow to stand for 3 hours and proceed as in (a). Results The results by this method in the presence of guanylurea salts are shown in the accompanying table. Biguanide nitrate Gram 0.2000 0.1000 0.0500 0.0100 0.0100 0.0100
3
Precipitate Gram 0.1582 0.0790 0.0394 0.0078 0.0078 0.0079
Recovery Per cent 100.3 100.2 100.0 99.0 99.0 100.0
The results are very satisfactory. I n every case the weight of the precipitate is within a fraction of a milligram of the theoretical results.
