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T H E J O U R N A L OF I S D C ’ S T R I A L A N D E N G I h r E E R I S G C H E M I S T R E - .
but also their after-effect upon one or two succeeding crops. I n the last column of the table is given the relative availability of the nitrogen in the different materials, arbitrarily considering 80 as the availability of the nitrogen of the dried blood (13.62 per cent. nitrogen), a n d deriving the availability of the nitrogen in the other materials from the increase in growth in each case over the appropriate check crops as compared with the increase caused by the dried blood. It is evident t h a t only such of these values as are based upon results with the same number of crops should b e strictly compared. The comparisons which should be emphasized in this connection are those concerning the availability of the nitrogen in the materials before and after being “acidulated, ” or subjected to the wet process. I t may be seen that although the availability gf the nitrogen is 33 in the unacidulated hair and 23 in the treated leather. the availabilities are increased t o 64 and 80, respectively, in the same material after being subjected to the wet process in the laboratory. The nitrogen in the garbage tankage, however, had a very low availability both before and after treatment. When the identical hair tankage, garbage tankage and treated leather, which were used in the fert.ilizer factory for the manufacture of the base goods, were applied to the pots in the same proportions as used in the works, the availability of the nitrugen was 49, whereas t h a t in the base goods made from the same materials was 84. About go per cent. of the nitrogen in the various unacidulated materials was insoluble in water, and although a half of the total nitrogen in the garbage tankage was still insoluble after acidulation, only about a fifth of the nitrogen in the acidulated roasted leather and hair tankage remained insoluble. That part of the nitrogen of the base goods which was rendered soluble by the wet process seems to have had an availability higher than t h a t in blood, whereas the insoluble nitrogen was practically useless. l‘egetation experiments to determine the availability of the nitrogen in such material as base goods, containing large amounts of available phosphorus, have to be conducted with every possible precaution to prevent the results being influenced by the phosphorus. The details of t h e consideration given t o this matter in the present instance would be out of place in this brief paper. The principle was followed of supplying phosphorus so liberally t h a t more mould be n-ithout influence on the crops. It may be seen by reference to the table t h a t when an extra amount of ;hosphorus was furnished in addition to the application of the dried blood, which served as a standard, no increase of crops resulted. Nevertheless, i t is best t o be conservative in comparing the nitrogen availability of highly nitrogenous non-phosphatic materials, like hair. leather and blood, with the same materials when existing in a mixture with a nitrogen content of less than 3 per cent, and with a high content of phosphorus. Furthermore, when such comparativelJ- small differences as exist in experiments of this 1iintE het7veen the n-eights of the crops from the check
443
and from the dried-blood pots are divided into 80 parts, i t is evident t h a t the “limit of error” is wide, and t h a t certainly a difference of less than I O in availability is of very little significance. I n view of these considerations, the claim is not made, therefore, t h a t the nitrogen in acidulated leather and base goods is as valuable as t h a t in dried blood. It is believed, however, t h a t the experiments prove the efficiency of the wet process, when properly carried out, for materially increasing the availability of certain low-grade nitrogenous materials. AGRICULTURAL EXPERIMENT STATION, KINGSTON, R. I.
NEUTRAL AMMONIUM CITRATE SOLUTION.’ By -4. J. PATTEX A N D C. S. ROBINSON.
Received January 12, 1912.
Since the proposal of the ammonium citrate method for the determination of available phosphoric acid, much trouble has been experienced in preparing a strictly neutral solution of the reagent. The weakness of both the acid and the base renders the end point quite indistinct with ordinary indicators, and much time and patience are required on the part of the operator to obtain the desired results. Several modifications of the simple titration method have been proposed, but each has objections which prohibit its common acceptation by practical chemists. The importance which the method has assumed in agricultural work demands, however, t h a t some convenient means be devised for preparing the necessary solution. Such a method has recently been proposed by Hall and Bell’ and was later shown by Hall3 to be quite suitable for laboratory use. At the time these articles appeared, the authors of this paper were engaged in working out the same method, and the results.are here offered, not with the hope of claiming the credit for originating the method, but simply as corroborative evidence in favor of its general adoption. Of the several methods proposed as substitutes for the present official method, t h a t recently suggested by Hand,4 using purified litmus solution or azolitmin, seems t o be the most promising. I n order t o test it out and compare it with the official corallin method as well as to obtain some data as to the accuracy of the latter an acid solution of ammonium citrate was made up and neutralized by these two methods by each of four analysts working independently. An acid citrate solution was chosen of, which 50 cc. required 7 . 5 0 cc. of the dilute ammonia solution for neutralization as determined by the conductivity method to be described later. The dilute ammonium hydroxide solution (about 3 per cent.) was kept in a burette enclosed in opaque paper to prevent the reading being taken until the supposed neutral point had been reached. I n this way each operation was made independently of the others. Great care was taken t h a t no loss of ammonium hydroxide should occur 1 Presented at the American Chemical Society Meeting at Washington, D. C., December, 1911. ~ J O U Y . Am. C h e n . S o c . . 33, 711 (1911). 3 THIS JOURNAL. 3, 559 (1911). 4 U. S. DeDt. of Agric., Bur. of Chem., Bull. 132, D. 11.
T H E J O V R n - A L OF ILVDUSTRI.4L A K D E I Y G I S E E R I S G C H E J f I S T R Y .
444
during the process.
The results are given in Tables
I and 11: TABLE1.
TABLE111. cc. dil. K H 4 0 H .
7
Kumber . P I... . . . . . . . . . 1 2 . 3 0 P 11.. . . . . . . . . . . 1 2 . 1 0 P 111.. . . . . . . . . . . 1 6 . 2 0 P IV... . . . . . . . . . 12.70 R I R I1 R 111.. 14.30 R I V . .. . . . . . . . . . 1 3 . 6 0
Kumber. M I... ?VI I1. . . . . . . . . . . . 11 111.. M I V .............
.........
..........
..........
I III... . . . . . . . . .
I IV. . . . . . . . . . . .
Per 5 0 cc. sol. 16.00 15.00 16.40 16.60 12.20 13.60 19.60 15.90
TABLEI1 With purified litmus as the indicator. Cubic centimeters dil. N H 4 0 H . Cubic centimeters dil. “,OH. -
Number.
P
R R R
Per 50 cc. sol.
111... . . . . . . . . . I. . . . . . . . . . . . 11.. . . . . . . . . . . I11
r
15.00
Sumber. M I.
16.00 15.00 17.50 14.00
hZ 111. I I I XI . . . . . . . . . . . . I I11
. . .
............
-
14.00 15.00 12.50 15.82 15.82 15.00
An inspection of these results reveals the fact t h a t the Official Method gives extremely inconsistent results even in the hands of one person. I n only one case was an exactly neutral solution secured. The variation in the results obtained by one analyst using this method amounted to seventy-four cc. of the dilute ammonium hydroxide solution per liter of the acid citrate solution. While this is the maximum variation in the four sets of determinations given, i t must, nevertheless be accepted as a possibility in actual practice. Such a condition is surely anything but derirable and demands immediate attention. The other method showed to much better advantage. Not only were the results more consistent, but one-third of the trials actually gave neutral solutions, These examples fairly illustrate the difficulty in making an exactly neutral reagent by the methods most in use, and it is quite possible that in many cases the character of the “neutral” ammonium citrate solution varies more than in the cases cited and t h a t considerable error may be introduced into determinations in this way. It is evident that not only is there a wide variation in the solutions made by different individuals, but that even the same person can rarely duplicate his own results. It has long been realized that i t was impossible t o get consistent results in neutralizing ammonium citrate solution by the Official Method, but i t has been assumed that the differences in the acidity of the solution were too small t o cause any appreciable error in the determinations made with them. In order t o test the correctness of this assumption, several actual determinations were made. The solutions used were R 11, C,I M IV, and 1111. They were carefully diluted to a specific gravity of I .09 and the determinations were all made at one time so t h a t there could be no variation due t o temperature of the bath. Determinations were made on two sam1
Neutralized by the conductivity method.
7
-
w
-
R I1. . . . . . . . . . . . 6 . 0 0
c . .. . . . . . . . . .
7.50
I 111.. . . . . . . . . . . 9 . 8 0 ‘
Sample I.
Sample 11. 7
7
Per 5 0 cc. sol.
Sumber.
11 I V . . . . . . . . . . . . 8 . 3 0
Per 5 0 cc. sol.
1912
ples of fertilizer, one containing a small percentage of insoluble P,O, and the other a large percentage. The results are given in Table I11 :
With corallin as the indicator. Cubic centimeters dil. N H 4 0 H . Cubic centimeters dil. S H 4 0 H . Per 5 0 cc. sol.
June,
-
Insol. Insol. P206. -4verP206. Per cent. age. Per cent. 2.84 2.81 2.83 3.54 3.80 3.74 4.23 4.07 4.21 4.79 4.77 4.90
v
Average.
8.86 2.83
8.84 8.82 9.82
3.69
9.81 9.80 10.10
4.17
10.04 9.98 10.56
4.82
10.46 10.36
An inspection of these results shows a marked relationship between the reaction of the ammonium citrate solution and the amount of phosphorus pentoxide extracted. These variations, amounting to I . 99 per cent. in one case and I . 6 2 per cent. in the other, are certainly significant. The results prove t h a t perfect neutrality of the citrate solution is of the utmost importance in securing consistent results, as the above differences are of sufficient magnitude to make the method extremely uncertain. CO K D U CTI V I T Y MET H 0D.
The above-mentioned method, proposed by Hall and Bell, was found to be much more satisfactory. I t depends upon the fact that when different quan-
C.ClQ m monia
F73.2. tities of alkali are added to an acid solution (or vice versa) the electrical conductivity or resistance of the
.
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1912
T H E JOCR.YdL OF I S D G S T R I A L A S D E.\7GI.\7EERISG
solution will vary with each addition, and if these resistances or conductivities are plotted against the amounts of alkali or acid added, there is a sharp change in the direction of the curve at the neutral
CHEXISTRY.
Cc. dil. “40H per 100 Bridge S O . cc. sol. readings. 1 10.0 542.25 15.0 545.i5 2 3. . . . . . . . . . . . 20.0 549.50
So.
......... ............
4.... 5.... 6....
S e u t. ACCURACY
fis. 2. point. This property has been made use of for the titration of various liquids where color changes were difficult t o observe and has given very good results. The method of procedure as given by Hall is quite satisfactory. A solution of citric acid is almost neutralized, the density being kept above I . 0 9 . Small samples of this solution are then titrated with a dilute solution of ammonium hydroxide, using corallin as an indicator, t o determine the approximate amount required t o neutralize the remaining acid. Definite quantities of the citrate solutions are removed with a pipette and transferred to clean, dry, volumetric flasks. To these portions of the original solution varying quantities of the dilute ammonium hydroxide are added in such a way t h a t some of the flasks contain more and some less than the approximate amount required for exact neutralization as determined b y the titration with corallin. These solutions are then made up t o the same volume with distilled water, placed in a thermostat, the temperature of which is held constant, and allowed t o come t o the temperature of the bath after which their resistances are measured by the Wheatstone bridge method. Plotting the cubic centimeters of ammonium hydroxide against the bridge readings gives a curve from which may be read the exact amount of ammonium hydroxide required t o neutralize the acid in a given quantity of the citrate solution. The following are some of the results obtained and illustrate the sharpness with which the neutral point may be read: TABLEIV.
NO.
1 ............ 2 3
............
............
Cc. dil. “,OH per 50 cc. sol. 0.0 7.0
14.0
Bridge readings. 525.75 533.50 539.75
Cc. dll. SHaOH per 50 Bridge No. cc. sol. readings. 4 . . . . . . . 21.0 539.00 5 . . . . . . . . . . . 28.0 538.25 6 !. 35 0 537.25 Xeut 14.0 539.75
.........
........
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Cc. dil. i\’H40H per 100 Bridge cc. sol. readings. . . . . 22.5 550.25 . . . . 25.0 550.00 . . . . 30.0 549.50 . , . . 21.6 550.35
O F METHOD.
I n order t o test the accuracy with ishich results may be duplicated by different operators, a stock solution of acid ammonium citrate was made up and neutralized independently by four laboratory assistants, three of whom had never before made any conductivity measurements. One hundred cubic centimeter portions of the acid solution were transferred t o 2 50 cc. volumetric flasks, the designated amounts of ammonium hydroxide added, and the bridge readings taken. Each operator made four sets of determinations on the same solution, the conditions being altered each time so as t o give different readings for each set, thus eliminating any error due to the operator attempting, unconsciously or otherwise, to duplicate his previous results. Each one was required t o plot his own results and report independently the amounts of ammonium hydroxide required t o neutralize the acid in the quantity of citrate solution taken. The results are given in the following table: TABLEv. Cc. dil. “,OH per 100 NO. cc. sol. P I.. . . . . . . . . . . . . 13.80 P 11... . . . . . . . . . . . 13.60 P 111... . . . . . . . . . . . 13.80 P IT‘.. . . . . . . . . . . . . 13.80 R I . . . . . . . . . . . . . . 14.00 R I1 . . . . . . . . . . . . . . 13.50 R 111. 13 .OO R IV 13.90
Cc. dil. NH4OH per 100 NO. cc. sol. .\I I... . . . . . . . . . . . 13.50 h l I1 . . . . . . . . . . . . . . 14.20 hl I11 . . . . . . . . . . . . . . 13.00 31 IT’.... . . . . . . . . . . 13.90 I I. . . . . . . . . . . . . . 13.50 I I1 . . . . . . . . . . . . . . 13.00 I I11. . . . . . . . . . . . . . 13.60 I I V . . . . . . . . . . . . . . 13.20
............. ..............
For the sake of comparison, averages of the several determinations made by each method are given in Table VI: TABLEVI. Average of
P series..
Corallin method.
................. .................
13.32 R series ................... 12.98 Y series.. 16 .OO I series.. . . . . . . . . . . . . . . . . . 15.32 Av. of all series.. .......... 14.41 Maximum variation. . . . . . . . 3.02 Maximum variation. . . . . . . . 1.59 Above ( + ) and below (-) average., . . . . . . . . . . . . . . . -1.43
+
Litmus method. 14.92 15.50 13.84 15.54 14.95 1.70 t0.59 -1.11
Conductivity method. 13.75 13.60 13.65 13.32 13.58 0.43 +0.17
-0.26
The determinations b y t h e corallin and litmus methods were made on the same solution, but the determinations by the conductivity method were made upon a solution of slightly different strength. The advantages of the conductivity method over the other two is well illustrated in the above table. The results b y the corallin and litmus methods are very variable, the greatest variation in the first case being 3 . 0 2 while in the second maximum variation is 1.70. The results by the conductivity method are very much closer, the maximum variation in the averages being only 0.43. If we assume the average of all the
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T H E JOURNAL OF I i l i D U S T R I A L AiVD E N G I N E E R I N G C H E M I S T R Y .
series, by this method, t o be the true result, then the maximum variation below this result is only 0.17 and t h e maximum variation above is 0 . 2 6 . These differences might well be considered within experimental error. RATIO O F AMMONIA TO CITRIC ACID.
Dr. McCandless, the referee on phosphoric acid for the Association of Official Agricultural Chemists, in 1909, suggested t h a t a reagent be used which should have the same ratio of ammonia t o citric acid as the pure triammonium salt. This ratio is I : 3.765. He made some cooperative tests with three other chemists, in which solutions were obtained having ratios Some time later the from I : 3.775 t o I : 4.189. Division of Fertilizer Chemists of the American Chemical Society recommended a solution in which the ratio of ammonia t o citric acid was I : 4 . 2 5 . A neutral solution was made up by the conductivity method and the ratio of ammonia t o citric acid determined. An average of three determinations gave a ratio of
I
I : 3.785. This would probably have approached still closer t o the theoretical ratio if the neutral solution had been made up immediately after making the conductivity measurements. During the several days that elapsed between the determinations of the quantity of dilute ammonium hydroxide solution required t o give perfect neutrality and the actual preparation of the neutral solution, the strength of the dilute ammonium hydroxide solution was probably changed. I t seems probable t h a t this method could be used t o give more satisfactory results than the present Official Method. COKCLUSIONS.
The present Official Method for preparing a neutral solution of ammonium citrate is extremely unreliable. The purified litmus method gives somewhat better results, although the limit of error is too great for reliable work. The conductivity method, on the other hand, is reliable and not difficult of operation and the results obtained by different workers agree very closely.
LABORATORY AND PLANT T H E MANUFACTURE OF GELATINE.' BY LUDWIGA. THIELE. Received Dec. 22, 1911. INTRODUCTION.
The manufacture of gelatine, originating in the remote past, when jelly was produced by boiling calves' feet in the kitchen, with the most crude and primitive methods, has now arrived a t such a state of perfection, through the application of chemical as well as engineering science, t h a t this industry may justly be proud of its progress. To-day gelatine is manufactured in millions of pounds, and plays a great role in the nutrition of the people. , While the bulk of gelatine is manufactured for edible purposes-for jellies, jams, for the candy industry and for ice cream, which product comes under the Pure Food Law-the gelatine used in the arts, for photographic dry plates and papers, for medical purposes in the form of capsules, for bacteriological purposes and for decoration of fancy goods, does not come under this law; nevertheless, all these varieties are made practically the same, with like care and precaution, from the most select raw materials, and under the most sanitary conditions which may be applied t o such a n industry. The manufacture of gelatine comprises the following distinct operations: I. Treating and cleaning the raw material. 11. Dissolving the gelatine. 111. Concentrating the gelatine solution. IV. Chilling and spreading. V. Drying. VI. Finishing (grinding and packing). The most important raw material consists of: a. Bones (osseine), hornpiths and button bones. 1 Presented a t the Fourth Annual Meeting of the .4merican Institute of'Chemica1 Engineers, Washington. Dec. 22, 1911.
June, 1912
1
b. Hidestock (calf-pates, trimmings and fleshings). ( a ) Osseine is the organic substance contained in the bones, the manufacture of which originates from France. Raw bones are not used in the manufacture of gelatine a t all, b u t have t o undergo a preliminary treatment in order t o produce osseine. The treatment for osseine and hidestock is then practically the same. Let us therefore first consider the pre' liminary treatment of the bones. Bones, as obtained either direct from the slaughterhouses in raw and wet state, or in dried form through dealers, have t o be washed, crushed and degreased in special extraction plants by means of benzine or carbon tetrachloride. I n this stage of manufacture, from 8 t o I O per cent. of bone fat is produced from the bones, while the water contained in the raw bones is nearly eliminated. The crushed, degreased bones no-- undergo the same treatment as the East India crushed bones, which contain practically no f a t , by extracting the mineral substance by means of diluted acids. This process, called maceration, produces about 60 per cent. of acid phosphate, a very valuable by-product. The acids t o be used in the manufacture of osseine are either hydrochloric, phosphoric or sulphurous, or, according to the process of Bergmann, hydrochloric combined with sulphurous acid. Until quite recently, the drawbacks attending the use of sulphurous acid prevented. its application in I n order t o prethe extraction of osseine from bones. vent the surface of the bones from becoming coated with a layer of tribasic calcium phosphate, i t was necessary t o keep either the liquid or the bones in constant motion. I n the Bergmann process these difficulties are obviated by causing the solution of sulphur dioxide to circulate through a battery of closed tanks in which the bones are treated, the solution being continually
