IAVDUSTRIAL -4h'D ELVGISEERI NG CHEMISTRY
852
yield figures could be obtained and those were usually on the unsatisfactory basis of cords of pulp wood. The manager must therefore wait until the inventory period to determine the effect of any voluntary or involuntary change in cooking conditions. By means of the determinations and calculations shown in Table I, it is now possible to determine pulp yields from the composition of the pulp and pulp wood with only the assumption of the mechanical losses. Such an analysis also shows the degree of hydrolysis to which the pulp has been subjected during cooking. The question might be asked whether the hydrolysis could not be performed on the pulp as well as on the cellulose isolated from the pulp. This can be done and the results used in the same sort of a calculation, provided that the lignin content of the pulp is also known. If, for instance, the loss of weight of a pulp on direct hydrolysis is 10 per cent, then the stable cellulose plus the lignin is 90 per cent, and if the lignin is 4 per cent, the stable cellulose is 86 per cent of the crude pulp. This figure for the stable cellulose can be used the same as before for comparison with the percentages of stable cellulose of the original wood to determine the yield of pulp.
1-01. 19, No. 7
Table I1 shows calculations from the same series of pulps used in Table I, but with the loss in weight on hydrolysis determined on the pulp itself. This figure was then combined with the lignin figure to give the yield of pulp. The yields are seen to correspond very closely to those obtained from the hydrolysis number of the isolated cellulose. Table 11-Calculation
of Pulp Yields from Direct Hydrolysis of the Pulp (Figures in per cent) UNHY-
DROLYZED
PULP SAMPLE 3131-1 3129-1 3128.1 3120-1 3130-1
Loss
ON HYDROLYSIS
7.91 10.07 9.02 9.53 10.20
RESIDUE LIGNININCLUDING FREE LIGNIN LIGNIN RESIDUE 92.09 1.80 90.29 89.93 4.50 85.43 90.98 3.20 87.78 90.47 3.40 87.07 89.80 4.20 85.60
CALCD ACTUAL PULP PULP YIELD YIELD 48.23 48.50 51.21 51.06 49.84 48.50 50.24 47.90 51.10 50.20
Hydrolysis number determinations will be valuable in many other places. Pulps prepared by the alkaline and neutral processes, different species of wood, heartwood and sapwood, springwood and summerwood, other cellulosic materials than wood-in the analysis of all these the hydrolysis number determination should be included.
Detection of Lactic Acid in Presence of Other Organic Acids' By Frederick G. Germuth DEPARTMENT O F PUBLIC WORKS,BCREAU OF STANDARDS, BALTIMORE, LID.
HIS research was und e r t a k e n in the interests of the Revision Program of the United States Pharmacopeia, following the suggestion of the committee in charge of this work as to the desirability of further investigation of reliable cheniical methods for the detection of lactic acid, particularly in the presence of other acids of organic origin.
T
Materials Used
A method has been described for the detection of lactic acid and lactates alone, or in the presence of other organic acids whose salts are largely employed for medicinal purposes. Lactic acid, in samples of 0.5 to 5 per cent concentration, in increments of 0.5 per cent, gives with 15 per cent solution of potassium thiocyanate (in the proportion of 0.5 cc. for each 1 per cent increase of lactic acid or lactate concentration) an orange or purplish coloration that is not discharged by saturated solution of mercuric chloride. Lactates treated in the same manner with the same proportions of reagents, and acidified with slight excess of concentrated hydrochloric acid, give with potassium thiocyanate solution an orange or purplish coloration that is not discharged by saturated solution of mercuric chloride.
The salts of organic acids employed in the experimental work and chosen as being those in whose presence lactic acid or lactates (see Table I) were most likely to occur were all of U. S. P. quality. S o attempt was made to purify these further as it is this grade of medicinals which the practitioner indicates when prescribing and also the grade employed by the manufacturing chemist in the production of various preparations. The potassium thiocyanate was of C. P. grade. It was recrystallized from slightly ammoniacal solution before use, then recrystallized twice again. The amount of iron in the original substance was thus reduced from 0.001 per cent to 0.0001 per cent. The colorimetric procedure was employed t o determine the amount of iron present. The other jmpurities were as follows: sulfuric anhydride, 0.001 per cent; ammonia, slight trace; chloride, 0.0001 per cent; and iron, 0.0001 per cent. The lactic acid was the C. P. product (sp. gr. 1.20, 68.5 1
Received February 28, 1927.
per cent) containing the following impurities : chloride, 0.001 per cent; sulfuric anhydride, 0.001 per cent. This xws carefully tested for iron content, and was found to contain about 0.0001 per cent of iron. Purification was accomplished by distillation a t greatly diminished pressure and subsequent redistillation. T h e p u r i f i e d product contained but a faint trace of iron, and traces of chloride and sulfuric anhydride. The calcium lactate was of U. S. P. quality and no attempt was made to eliminate impurities with the exception of the iron. This was accomplished by solution of the salt and the regular precipitation method. The iron was reduced to less than 0.0001 per cent, as determined by the potassium ferrocyanide method. Method
The procedure consisted in preparing 5 per cent solutions of each of the compounds under consideration, and subsequently treating each sample with chemical reagents of the concentration generally employed in qualitative analysis. The results are given in Table I. These reactions indicated the improbability of identifying lactic acid or a lactate in the presence of other organic acid anions. A series of experiments was made to prove this, however, using a mixture comprising all the salts used in the previous experiments. The results are shown in Table 11. I n the foregoing experiments those compounds were em-
July, 1927
I S D C S T R I A L B S D E S G I S E E R I S G CHEMISTRY Table I-Reactions
COMPOUXD AZNOd Lactic acid Black ppt." ... Citric acid Tartaric acid TVhite ppt. Sodium phosphate Yellow p p t . Sodium phosphite Black ppt.b Brown p p t . Sodium hypophosphite ... Sodium succinate Sodium butyrate ... Sodium benzoate ... Sodium salicylate ... Calcium lactate Bronnc Zinc sultocarbolat e ... Potassium citrate ... Zinc valerate Sodium potassium t a r t r a t e Uhite' Ammonium acetate Black ppt. a These reactions occurred when KOH was added b Reduction t o 4g. c Boiled with slight excess of KOH solution
White'ppt.
...
...
...
Reddish brownc
... ...
...
Black'ppt. t o neutralization
REAGEKT AgSCh Hg2(503)2
Pb(CZH30d2 SnCln MgSO, HgCh SbCl,
of Mixtures of Organic .4nions REACTION h i a n y colored ppt. Brown ppt. No p p t Turbid Slightly turbid Turbid Brown coloration
A solution of all the chemical compounds employed was then prepared, and on addition of the potassiurn thiocyanate reagent the color was again produced, and remained on adding a solution of the mercuric salt. 1 solution was next prepared containing each of the salts with the exception of lactic acid or calcium lactate. Upon treating this in the same manner as the other it remained colorless. A portion of the hydrochloric acid used wis distilled to free i t of the amall amount of iron present, to ascertain what effect, if any, this might have on the test. Solutions of' 0.5 to 5 per cent lactic acid, prepared in increments of 0.5 per cent concentration, were then treated with potassium thiocyanate solution. The color was readily discernible in the test tube containing each concentration, and each retained its color upon addition of mercuric chloride solution. A separate sample of the hydrochloric acid used during the tests was treated in the same manner, but the amount of iron salts present was so small that a coloration was not produced on adding the reagent. Solutions of calcium lactate acidified with concentrated hydrochloric acid mere prepared and the same procedures followed as in the lactic acid determinations. Each of these, in turn, was treated with the potassium thiocyanate reagent. The same orange coloration (purplish in the more concentrated solutions) was obtained as in the former experiment, and re-
hlgSO,
SnCh
...
D a r k color
...
Turbid
...
Turbid
... ... ...
. .
...
. o
... / . .
...
... ...
...
... ... ...
...
D a r i color
ployed as reagents in which the base was calculated to combine chemically with the anion of lactic acid or a soluble lactate t o produce a lactate of the metal present in the salt used. I t occurred to the author, however, that in a number of instances chemical compounds had been detected by reagents which brought about an interaction between the acid radicals of the substances in question rather than a chemical reaction of the metathetical type. An example of this is the detection of sulfides by sodium nitroferricyanide, which produces a purple shade of some intensity. After unsuc.cessfu1 attempts to identify lactic acid or a lactate with several reagents, on adding 2.3 cc. of 15 per cent potassium thiocyanate solution, it was found that with lactic acid and calcium lactate (acidified with hydrochloric acid) a coloration was produced which varied from an orange shade to a purple depending on the concentration of the solution. With all the other compounds there was no visible reaction. It was at first believed that this coloration might be caused by minute portions of a ferric salt. On the addition of a saturated solution of mercuric chloride, however, the shade did not disappear, as would have been the case if a ferric compound had been present. Table 11-Reactions
of Organic Anions
(Dots indicate no precipitate) He,,(NOd? Pb(C?H30?)? _ . Black ppt." .,.
. .
8 53
...
,..
... ... ... ... ...
...
Turbid
HgCln
...
...
... ... ... Turbid
... ...
... ...
... ...
Turbid
,..
Slight'color
...
...
...
niained inert as regards color upon addition of saturated solution of mercuric chloride. Experimental solutions of ferric chloride were made, duplicating the intensity of shade produced in the solutions of lactic acid and the lactate by the employment of potassium thiocyanate. Cpon treating these solutions in the same manner as the solutions utilized in the research, the color was immediately dispatched upon adding the mercuric chloride solution. The next step consisted in dividing into two portions, 30 cc. of a mixture of the organic salts including calcium lactate. Each portion was placed in a medium-sized test tube. To the first was added the standard amount of potassium thiocyanate solution (first acidifying with concentrated (sp. gr. 1.20) hydrochloric acid) followed by solution of mercuric chloride. To the second test tube were added several drops of a 10 per cent solution of ferric chloride. Upon addition of the potassium thiocyanate solution to this portion, a deep red, bordering almost on black, was discerned. To this an excess of the mercuric chloride solution was added, and immediately the intensity of color due to the presence of undissociated ferric thiocyanate disappeared, while the color imparted by the lactate remained. Cpon comparison, it was found that the depth of shade of the color in the solutions of both tubes was identical. Samples prepared containing an amount of iron equal to that present in the purified reagents gave an almost iniperceptible color with the potassium thiocyanate, which was immediately discharged on addition of saturated mercuric chloride solution. Discussion of Results
Upon adding a solution of potassium thiocyanate to lactic acid or a lactate, it is believed that sulfonation, using the term in a broader sense than that generally implied, takes place a t the expense of the potassium salt, forming a substitution product of lactic acid, which causes the coloration. The best results are obtained when the potassium thiocyanate reagent is of 15 per cent strength (an additional 0.5 cc. being added for each increase of 1 per cent) and the amount of concentrated hydrochloric acid is slightly in exceSs of neutrality, using a 15-cc. sample for the test. This method of detection is not affected by heat, as the color is quite stable and as distinct in hot solutions as in those of lower temperature. No attempt was made t o ascertain to what extent this method might be applied to the quantitative determination of lactic acid and lactates, by colorimetric procedure. EKperimental work of this nature may be considered later. Acknowledgment
Grateful acknowledgment is made of the assistance rendered by Charles R. Preston, head of the standardization division of this bureau, in the form of helpful suggestions and constructive criticism.
