INDUSTRIAL A N D ENGISEERIiL'G CHEMISTRY
May, 1925
plants. -4mong the diseases or insect pests which might be combated successfully by means of such sprays are pear blight, oyster-shell scale, blister canker, crown-gall, and the like.
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3-Selenium compounds are deleterious to certain plants such as dandelions, plantain, burdock, etc., while the injury to grass and clover is less severe; hence these chemicals may prove useful as weed eradicators.
The Determination of Cyanamide' By L. A. Pinck FIXEDNITROGEN RESEARCH L,4BORATORY, ~ ' A S H I N G T O Z I ,D.
ET'ERAL methods and many modifications have been proposed for the quantitative determination of cyanamide. Nearly all of them are based on the precipitation of cyanamide as a silver salt, and the determination of the cyanamide on the basis of nitrogen or silver.
S
Previous Methods
I,
c.
low in others, That the solubility of the silver cyanamide, either in the solution from which it was precipitated or distilled water, was not in part responsible for the unsatisfactory results was soon demonstrated, and hence attention was directed to the effect of the presence of various quan& ties of cyanamide deriua-1 tives.
Perotti2 first developed Experimental In the course of an investigation at this laboratory a titration method consiston cyanamide and some of its derivatives, unsatisfacA serieb of cyanamide ing in the addition of an amtory results were obtained in the quantitative deterdeterminations was theremoniacal extract of calcium mination of cyanamide, particularly in the presence of fore made on crude calcium c y a n a m i d e to a definite relatively large amounts of derivatives, such as dicycyanamide extracts to which quantity of silver nitrate anodiamide, urea, guanylurea, and guanidine. A study varying amounts of urea, solution, the filtration of the was therefore made of the effect of various concentraguanylurea sulfate, guanisilver cyanamide precipitions of these compounds on the determination of dine nitrate, and dicyanotate, and the titration of the cyanamide in the two most promising analytical diamide were added. To excess sil\,er nitrate with methods. The results of this study are briefly presented each 50-cc. aliquot of crude standard thiocyanate solutogether with a description of an analytical procedure calcium cyanamide extract, t i o n . K a p p e n 3 modified for cyanamide which was developed and has been found containing approximately this method by acidifying to be very satisfactory in the work at this laboratory. 50 mg. of cyanamide nitrothe cyanamide solution to convert the calcium into 1; 11 gen, ,: 25>50, and 100 mg. a neutral s a l t a n d t h e n of t h e a b o v e substances adding a slight excess of ammonia. He also stipulated the were added. The results are given in Table I. Since use of dilute solutions. Grube and Kriiger4 modified the the first set of results on the extracts containing dicyanodiKappen method by adding the silver nitrate to an acid solu- amide was divergent, that set was repeated. tion and then making it ammoniacal. In the Caro methodb of Various Cyanamide Derivatives on Determination the precipitation was made with an ammoniacal silver ace- Table I-Effectof Cyanamide by t h e Caro-Brioux Method tate solution and the cyanamide was determined by kjel- Material added P E R CENT CYANAMID€ N A S DETERMINED I N PRESENCE OF t O 0.25 gram dahling the silver cyanamide precipitate. BriouxG modicrude CaCNz Guanylurea Guanidine rDicyanodiamideGram Urea sulfate nitrate 1st set 2nd set fied the Caro method by using silver nitrate instead of the 19.12 18.97 18.87 18.95 18.87 None acetate and titrating silver in the silver cyanamide. Anot'her 1 9 . 7 6 19.58 0,005 19.09 18.97 18.92 \20.86 21.59 method, consisting in the hydrolysis of cyanamide to urea 0.025 19.13 19.15 19.07 20.38 21.66 and the determination of the latter, had been proposed by a 120.65 21.66 21.70 21.48 number of investigator^,^ but the writer did not find that 0.050 19.20 19.24 19.29 method quantitative. Marquerol and co-workers8 made a 20.20 22.90 comparative study of most of the methods and found them 0.loo 19.24 19.29 19.44 22.55 22.08 22.54 22.37 all to be inaccurate: however, the Car0 method gave the best results. These results show that the method is not reliable for samThe method employed in the early work of this laboratory ples containing large amounts of cyanamide derivatives, was a combination of the Car0 and Brioux methods (hereafter referred to as the Caro-Brioux method), consisting of dicyanodiamide interfering most. The development of a volumetric method in which cyanthe addition of silver nitrate solution to an ammoniacal solution of cyanamide and t'he determination of the nitrogen amide derivatives would not interfere was then undertaken. in the silver cyanamide by the Kjeldahl-Gunning method. To a 50-cc. aliquot of crude calcium cyanamide extract there The results were unsatisfactory, being high in some cases and were added 1 cc. of concentrated ammonium hydroxide and varying amounts of ammoniacal silver nitrate solution. 1 Received March 7. 1925. The silver cyanamide precipitate was filtered off a t the end Gas. chim. ita2., 36, 11, 230 (1905). of 2 hours. The silver was determined either in the filtrate 3 Landw.Vers.- Sla., 70, 455 (1909). or in the precipitate by means of potassium thiocyanate 4 Z . angew. Chem., 87, I, 326 (1914). ' Ibid., 8 3 , 2405 (1910). in acid solution. The Caro-Brioux method was used as a ' A n n . sci. agron., April, 1910. check. Table I1 shows the results obtained with different 7 Monnier, Chem. Z l g . , 86, 601 (1911); Fosse, et a l . , c ' o m p f . r e n d . , 179, samples of calcium cyanamide (or mixtures containing cyan408 (1924). amide) and with varying amounts of silver nitrate. 6 .Ann. chim. anal., [2] 2 , 164 (1920).
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Vol. 17, No. 5
INDUSTRIAL A X D ENGINEERING CHEMISTRY
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Table 11-Comparison of Caro-Brioux and Volumetric Methods Using Varying Amounts of AgN03 VOLUMETRIC METHOD CARO-BRIOUX Excess METHOD 0 . 2 5 K Per cent AgN03 Per cent SAMPLE cyanamide N Cc. cyanamide N REMARKS 1 Crude 18.09 1 18.03 18.03 2 18.07 CaCNz 18.12 19.32 2 19.32 19.28 2 Crude 6 19.30 19.30 CaCNz 19.32 65.03 6 65.02 65.21 3 HEN, 4 Crude CaCNz 3.73 1 3.65 3.67 +Kzs01 3 . 7 5 5 3.75 3.74 5 Crude CaCNz +KC1 2.36 1.71 1 . 7 1 4 . 9 1 7 dicyanodiamideN 1.~ 2 urea % N 6 Crude 7.34 3 6.46 6 44 4 8275dicyanodiamideN CaCNz 7.45 6 6.44 61431 2:24%urea N
...
..
This table shows that the results of the two methods are in very close agreement for samples of cyanamide which do not contain any dicyanodiamide or urea, but that they differ in the presence of these compounds. Moreover, the results are constant with varying amounts of ammoniacal silver nitrate. A comparison of the two methods was then made on a cyanamide extract and on the same extract to which dicyanodiamide and urea had been added. The composition of the latter solution was approximated as follows: cyanamide nitrogen, 15 per cent; dicyanodiamide nitrogen, 75 per cent; and urea nitrogen, 10 per cent. The results are shown in Table 111. Table 111-Determination of Cyanamide in Solutions Having a High Concentration of Cyanamide Derivatives (Figures in per cent) CYANAMIDE SOLUTION CONTAINING DICYANODIAMIDE A N D UREA CYANAMIDE SOLUTION ALONE Caro-Brioux Volumetric I-Caro-Brioux MethodVolumetric Kjeldahl N method method Ag titration method 22.98 22.43 19.68 19.22 19.25 23.82 21.87 19.64 19.15 19.17 22.36 23.25 19.64 19.22 19.22
These results again indicated that by the Caro-Brioux method of precipitation of silver cyanamide in the presence of dicyanodiamide some silver dicyanodiamide was also precipitated. Kappen3 found that his method was quantitative for pure cyanamide or calcium cyanamide not containing any other nitrogenous compounds and that dicyanodiamide interfered most. The volumetric method also gave results somewhat too high (0.4 per cent), and it was therefore concluded that reprecipitation was necessary. This was effected by dissolving the filtered and washed precipitate with dilute nitric acid and reprecipitating by the addition of ammonium hydroxide. Low results were occasionally obtained, however, owing to the combined solvent action of the ammonium nitrate in the presence of excess ammonia, previously pointed out by Grube and Kruger,4 and as shown by the following experiment: Cyanamide determinations were made by the volumetric method on 50-cc. aliquots of a crude calcium cyanamide extract to which 2 grams of ammonium nitrate were added. T o one sample the usual excess of a,mmonia was added while in another the cyanamide was precipitated without the addition of ammonia. The results are given in Table IV. Table IV
SAMPLECONTAINING No NH4NOa 2 grams NHnNOa 2 grams NHnN03
+ 1 cc. “,OH
Per cent cyanamide N
{;::E 20.52 20.70
That the solvent action of ammonium nitrate could be reduced by proper dilution was shown by an experiment in which 2 grams of ammonium nitrate were added to 25-cc.
aliquots of cyanamide solution. One solution was diluted with 100 cc. of water, another with 200 cc., and then 40 cc. of 0 1 N ammoniacal tilver nitrate were slowly added to each. The precipitate was filtered, dissolved, and titrated in the usual manner. The results are shown in Table V. Table V SAMPLE CONTAININQ No NH4NOa 2 grams NHdNOa and diluted with 100 cc. HzO 2 grams NHdNOs and diluted with 200 cc. H i 0
Mg
.
cyanamide N
I;,58.5
Is::
5
--.I
58.6 L3.7
Reprecipitation with the proper dilution was tried on the solution previously mentioned, containing 15 per cent of the nitrogen in the form of cyanamide, 10 per cent as urea, and 75 per cent as dicyanodiamide. The cyanamide determination checked very closely with the amount of cyanamide put in the solution, the potassium thiocyanate titration for cyanamide alone being 8.83 cc. and that for the solution containing dicyanodiamide and urea, 8.85 cc Method
A 2-gram sample of crude calcium cyanamide is extracted for 2 hours with 400 cc. of water in a shaking machine. -After filtering, 50-cc. aliquots are pipetted into 250-cc. beakers, 1 cc. concentrated ammonia is added, and ammoniacal silver nitrate run in with constant stirring from a buret a t such a rate that the drops can be counted very readily. If the sample is in solution, an aliquot equivalent to about 50 mg. nitrogen is taken for analysis. After standing for 15 minutes the precipitate is filtered off through a Gooch crucible containing an asbestos mat. The silver cyanamide precipitate is washed eight to ten times with distilled water, then dissolved with dilute nitric acid (approximately 1 N ) and titrated with standard thiocyanate solution in the presence of ferric alum indicator. I n the presence of a very large amount of dicyanodiamide it is necessary to redissolve the silver cyanamide precipitate in dilute nitric acid. This can easily be accomplished by running dilute nitric acid (not over 25 cc. normal acid) through the Gooch containing the silver cyanamide with the use of suction. The Gooch is well washed with distilled water. Reprecipitation is made by first diluting the solution to 150200 cc. and then adding a few cubic centimeters of ammoniacal silver nitrate and as much ammonia as is necessary to make the solution barely alkaline. The solution is well stirred, and after standing for at least 2 hours it is filtered, the precipitate washed, dissolved, and titrated with standard potassium thiocyanate as described above. If carbide is present in the sample it is necessary to kjeldah1 the silver cyanamide precipitate instead of titrating it. Japanese DyestufI Subsidy Continued-Accordin: to a cable received from Acting Commercial Attache Rhea, Tokyo, the Japanese Diet, before its adjournment on March 31, passed an act encouraging the Japanese dyestuffs industry. The act carries a subsidy not to exceed 1,000,000 yen per year, for six years (I yen =$0.416, a t the exchange prevailing April 2 ) , which is about one-half the former figure. The government has been guaranteeing an 8 per cent dividend on the stock of the Nippon Senryo Sciso Kaisha (Japan Dye Manufacturing Company), which has been subsidized to the extent of approximately 2,000,000 yen yer year. It is said that as many as sixty varieties of coloring materials have been manufactured, of which only about thirty-five have proved successful. There has been a tendency to import the more expensive and complicated dyes, and t o manufacture the cheaper and less difficult. Imports of dyes into Japan have been very heavy during the past year, and it has been impossible for domestic dyes to coinPete in the market on either a color or a price basis.
