42
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
A PROPOSED RAPID METHOD FOR THE ANALYSIS OF LIMESTONE FOR AGRICULTURAL PROCESSES’ By A. S. BFHRMAN Received April 19, 1915
The object of this work was t o devise a method for the analysis of limestone, which would be shorter t h a n other procedures now in general use, and which would be sufficiently accurate for agricultural requirements. By “sufficiently accurate” we may more or less arbitrarily designate a limit of error of one per cent from the t r u e value of t h e three agriculturally important factors-( I ) insoluble residue and ammonia precipitate, ( 2 ) calcium carbonate, (3) magnesium carbonate. A perusal of standard references and current literature revealed no information pertinent t o t h e present subject. T h e most helpful suggestion was derived from a n unpublished method developed b y Mr. S. D. Averitt, of t h e Kentucky Agricultural Experiment Station. This differential method assumes t h a t t h e s u m of t h e percentages of the insoluble residue (from digestion in dilute hydrochloric acid), the ammonia precipitate weighed as aluminum a n d ferric oxides and t h e calcium and magnesium carbonates is 100. If a qualitative test shows considerable magnesia present, t h e calcium carbonate is determined b y t h e usual oxalate method. This percentage subtracted from t h e total carbonates yields t h e percenfage of magnesium carbonate. If, however, t h e qualitative test shows no more t h a n about 5 per cent of magnesium carbonate, t h e calcium is not determined. The figure of the combined carbonates is then reported as calcium carbonate, with a qualitative statement as t o the estimated amount of. magnesium carbonate present. Although t h e above procedure reports as calcium or magnesium carbonate a n y inclosed or combined water, this error has been shown t o be insignificant by comparative analyses made a t t h e Experiment Station. The methods of analysis as ordinarily used have been employed for comparative purposes in this work. These will be found in a n y of t h e standard,references, such as Fresenius, Treadwell, Talbot and Sutton. EXPERIMENTAL
The experimental portion of this work may be divided into two parts, each representing a distinctly different a t t e m p t t o arrive a t the solution of t h e problem under consideration. SERIES I
The first method sought t o make use of t h e fact t h a t pure calcium carbonate is very rapidly soluble in dilute hydrochloric acid and magnesium carbonate slowly soluble, while dolomites and magnesium limestones have a time solubility t h a t varies with t.he proportion of magnesium carbonate present. The object here was t o see if such a variation was a quantitative one a n d if so, whether t h e time taken for solution of a definite weight of t h e sample could not be used a s a n estimate of t h e amounts of calcium and magnesium carbonates present, when compared 1 Owing t o the departure of the author for the Philippines, i t was impossible for him to give further time t o the development of this method and this record is presented in the hope t h a t it may give an impetus t o similar experimentation looking towards an entirely volumetric method for the agricultural analysis of limestone.
Vol. 8, NO,I
with t h a t required for t h e solution of t h e pure carbonates. The experiments detailed in Table I were carried out using 80/1oo mesh calcite (99.5 per cent calcium carbonate) and magnesite (97.6 per cent magnesium carbonate) weighed out on a rough reagent balance into Erlenmeyer flasks. The stated amounts of hydrochloric acid were put into each of two beakers, heated on the steam bath, and when the highest temperature of the bath was reached (86’ C.), the acid was poured into the carbonates. The flasks were kept on the bath and the solution periods taken with an ordinary watch. TABLEI Flask used No. Cc. 1 . . . . . . . , . , 300 2. ,,, 300 3 . . . . ., . , 300 4 . . . . . . , . . . 1000 5 . . . . . . . . . . 1000
.... . . . .
Acid used Cc. 50 100 200 500 500
yo increase Charge of magStrength of Minutes required nesite of carbonate for solution of over acid Grams Calcite Magnesite calcite N 1.0 0.75 3.0 300.0 N/2 1.0 5.5 9.0 63.5 1.0 8.0 12.0 50.0 1.0 17.0 23.0 28.2 N/16 0.5 16.0 20.0 25.0
$5;
The results in Table I brought out the interesting though disturbing fact, t h a t , as t h e dilution of t h e acid increases, t h e lengths of time required for the solution of equal weights of calcite and magnesite approach coincidence. Since dilute acids must be employed, however, in order t o secure a sufficiently long time for measurement, it is evident t h a t t h e uncertainty of t h e time element precludes t h e use of the suggested method as a means of analysis. S E R I E S I1
T h e impracticability of the method suggested in Series I having been demonstrated, a more purely chemical procedure was next sought for. Without entering into the numerous difficulties encountered, which frequently necessitated extensive modifications of the proposed method, the final procedure adopted will first be stated, followed by the theory and experimentation in support of it. NETHOD
One gram of the rather finely crushed sample is weighed into a zoo cc. Phillips beaker. I n t o this is now carefully pipetted j o cc. of standard N / 2 hydrochloric acid, followed b y a few drops of a 3 per cent hydrogen peroxide solution. il small porcelain crucible is now set loosely in the top of t h e beaker, and t h e whole placed on t h e mater bath. After remaining a t this b a t h temperature (86’ C.) for 30 minutes, t h e beaker is removed from the b a t h and cooled. When almost or completely cooled, 5 grams of dry ammonium chloride are added and dissolved by agitation: some macerated filter paper is also introduced: 2 j cc. of a standard N / 2 ammonium hydroxide solution are then added slowly with shaking. The beaker is stopped with a rubber stopper, agitated well and let stand for I j minutes. Filtration is now made as rapidly as possible through an ashless filter into a 3 5 0 cc. Erlenmeyer flask, and the precipitate washed thoroughly with a neutral I O per cent solution of ammonium nitrate until all the ammonia is in the filtrate. The precipitate is ignited and weighed. The weight thus obtained represents the insoluble residue, plus t h e aluminum and ferric oxides. The filtrate and washings from t h e insoluble residue and ammonia precipitate are titrated with standard
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
Jan., 1916
N / 2 hydrochloric acid, using methyl orange as a n indicator. From t h e hydrochloric acid required t o p u t t h e carbonates into solution, a n d from t h e total carbonates (found by subtracting t h e insoluble residue a n d ignited ammonia precipitate from IOO),can be calculated t h e percentages of calcium and magnesium carbonates present.
THEORETICAL
is a rough, though conservative estimate of t h e distribution of time taken for analysis: Hrs.
Ignition and weighing of residues..
.. . , . . . . . . . , . . . , . , . . . . . . , . , . , . .
TOTAL
The assumption employed in t h e “differential” method of t h e Kentucky Agricultural Experiment Station is also used here, t h a t we may find t h e combined percentages of calcium and magnesium carbonates by subtracting t h e percentage of insoluble residue and ignited ammonia precipitate from 100. If X = grams of calcium carbonate, Y = grams of magnesium carbonate, A = grams of calcium carbonate plus magnesium carbonate, a n d B = grams of COa in both carbonates, then: X Y = A , and 0.j9946X o.71157Y = B . A is known, being found by subtraction of t h e insoluble residue and ignited ammonia precipitate from 1.0000,as above. B also is known: I cc. of N / 2 acid is equivalent t o 0.015 g. of C O I . This value, multiplied by t h e number of cc. of N / 2 acid required to put t h e calcium a n d magnesium carbonates into solution, yields t h e value B in t h e second equation.
+
43
+
,.,
1.25
4.00
NOTES ON DETAILS OF MANIPULATION, ETC.
1-In the proposed method, a dilute solution of hydrochloric acid is heated on the water bath for 30 minutes. To determine whether, under these conditions, there is any loss of HCl, ten zj cc. portions of N / z hydrochloric acid were pipetted into as many Phillips beakers and a crucible set loosely in the top of each. Five of these portions were diluted to about 50 cc. with cold distilled water, and titrated with N / z potassium hydroxide solution, using phenolphthalein as an indicator. The other five portions were placed on the water bath, allowed to remain a t the bath temperature (86’) for 30 minutes, cooled, diluted t o about 50 cc. with cold distilled water, and titrated with 0.5 N potassium hydroxide. The results were as follows: FORPORTIOKS N o t heated Heated..
.. ..
Cc. N/2 K O H required
.....
25.45 25.47
25.48 25.45
25 45 25.48
25.46 25.48
25.47 25.45
Evidently no hydrochloric acid was lost by volatilization. This was very welcome information in view of the fact that experiments had shown that the non-volatile sulfuric acid could not be used, due to the large amount of calcium sulfate which Suppose, to take a concrete example, a one gram sample was was formed, and which was not entirely soluble even in the presence of an excess of ammonium salts. dissolved in jo cc. of N I P hydrochloric acid, the ammonia z-The function of the 5 grams of ammonium chloride is to precipitation was made with 2 5 cc. of N / z ammonium hydroxide, and to titrate the excess of ammonia in the filtrate from the inhibit the precipitation of any calcium-and less probably any might be re-formed by the carbon ammonium hydroxide requires 15 cc. of N / z hydrochloric acid. magnesium carbonate-that Evidently then, 40 cc. of N / 2 acid were required to put the dioxide retained in solution when the same is made alkaline calcium and magnesium carbonates into solution, and this during the ammonia precipitation. To obtain definite information on this point, four 1.0000gram charges of pure precipitated 40 cc., therefore, represented 0.600g. COa. 0.59946 is the factor for converting calcium carbonate to COS. calcium carbonate, free from iron and aluminum, were dissolved in 50 cc. of N I Phydrochloric acid in loosely covered Phillips beakers, 0.71157is the factor for converting magnesium carbonate t o and placed on the water bath. After remaining a t bath temcos. perature for 15 minutes two of the beakers were removed. To When the two simultaneous equations are solved, we find that one of these ammonium hydroxide was added to alkalinity. 0.71157 A - B B - 0.j9946 A X = and Y = A heavy precipitate of calcium carbonate resulted. To the 0.1 121 I 0 . 1 1 2 1I other, before making alkaline, 5 grams of dry ammonium chloride i. e., the grams of calcium carbonate may be found by sub- were added; when this solution was made alkaline with ammotracting the total weight of COSfrom 0.71157,the weight of the nium hydroxide, only a very light precipitate occurred. The combined carbonates, and dividing the result of this subtraction other two beakers were allowed to stand on the bath for 30 by 0 . 1 1 2 1 1 . minutes. At the expiration of this time, the contents of one The magnesium carbonate may be found either in the manner beaker were made alkaline with ammonium hydroxide; a marked Y = A . precipitation of calcium carbonate resulted. To the other of solving for Y shown above, or from the equation X beaker was first added 5 grams of dry ammonium chloride, A D V A N T A G E S OF THE M E T H O D P R O P O S E D followed by ammonium hydroxide to alkalinity : no precipitation The chief advantage of t h e proposed method, if of calcium carbonate occurred, even upon standing. As this proven practical, would be in t h e saving of time a n d was the condition desired, and as time did not permit further t h e number of operations required in t h e determina- investigation, no attempt was made to derive any quantitative tion of the three values ordinarily reported in agri- data on this point. To determine whether or not this inhibition would take place cultural analyses of limestone, viz.: ( I ) Insoluble residue and ferric and aluminium oxides, (2) calcium under conditions of actual analysis, as well as in the blanks, four 1.0000 gram charges of sample No. 8 were analyzed for the carbonate, (3) magnesium carbonate. By t h e judicious distribution of time, and with proper insoluble residue and ammonia precipitate. Nos. I and z were equipment, i t is easily possible t o analyze 8 samples each digested with 2 5 cc. of hydrochloric acid (sp. gr. I.IZ), a few drops of 3 per cent hydrogen peroxide solution, and boiled for t h e three above factors in 4 hours-something well to expel all carbon dioxide. After a slight cooling, some which, in t h e writer’s opinion, can not be done by a n y macerated filter paper was added, followed by ammonium of t h e methods now in general use. hydroxide to alkalinity. After about IO minutes digestion just The following, expressed in decimal parts of a n hour, below the boiling point, the precipitate was transferred to a
+
T H E JOCRATAL O F IhTDlJSTRIAL A N D E N G I N E E R I N G C H E I M I S T R Y
44
quantitative filter paper, washed well with hot neutral ammonium nitrate solution, ignited and weighed. Kos. 3 and 4 were digested on the water bath for 30 minutes with j o cc. N / 2 hydrochloric acid, with a few drops of 3 per cent hydrogen peroxide solution. .4t the expiration of this time, 5 grams of ammonium chloride were added, followed by somc macerated filter paper and then by ammonium hydroxide to alkalinity. After agitating well and allowing to stand a few minutes a t room temperature, the precipitate was transferred to a filter, and 6reated from this point on, as before. The comparative results fol101v: Grams Insol. Res.
+ Amm. P p t . . . . . . "
1 2 0,1014 0.1016
3 0.1015
4 0.1016
3-It will be noticed that the ammonia precipitation is made cold. This is due to the fact that, a t the temperature of the water bath, some ammonia is lost from the N / z ammonium hydroxide solution, as was shown by the following experiment: Six I O cc. portions of iV/z hydrochloric acid were pipetted into Phillips beakers, and diluted to about j o cc. with distilled water, Three of the beakers, covered with crucibles, were placed, on the water bath, and when a t bath temperature 2 j cc. N / z ammonium hydroxide were added. After rapid cooling, the excess of ammonia mas titrated with N/z hydrochloric acid. To the other three beakers, which had not been heated, were also added z j cc. of iV/z ammonium hydroxide and, as before, the excess of ammonia titrated with N / z hydrochloric acid. The comparative results follow: PORTIONS Cc. of alkali reauired S o t heated . . . . . . . . , . . , . 14.36 14.32 14.34 Heated . . . . . . . . . , , , , . , 14.10 14.12 14.15
Evidently, then, the ammonia precipitation must be made cold, if the proposed method is to be employed. To ascertain if the precipitate obtained under these conditions corresponds to that obtained under more favorable circumstances, three 1.0000 gram charges of the same sample used in (2) were digested on the water bath for 30 minutes with 50 cc. N / z hydrochloric acid, and a few drops of a 3 per cent solution of hydrogen peroxide added. At the end of 30 minutes the beaker was removed from the bath, and cooled rapidly ,by agitating in cold water. Five grams of dry ammonium chloride were then added to each beaker, followed by some macerated filter paper, and then by 25 cc. of N / z ammonium hydroxide. After agitating well, the precipitate was allowed to stand for I j minutes, then filtered, washed, ignited and weighed as in (2). The weights follom: As made a b o v e . , . . . , . . . . . . . . . 0.1014 Average as derived in (2). . . , . .
0.1012
0.1013 0,1015
Evidently, then, under the conditions of the proposed method, the ammonia precipitation is practically complete. g-The function of the hydrogen peroxide is, of course, to convert all iron present to the ferric. condition, to insure its complete precipitation. 5-No error arises from the fact that the iron and aluminum compounds require some acid for their solution, for, since the iron and aluminum are precipitated before titration, only that acid that has been used up for solution of the calcium and magnesium carbonates will be determined. APJALYSES
Practically all of the experimental work was done on 13 limestones, 8 of which approached dolomite in their high magnesian content. Duplicate analyses, reported in Table 11, were made of all these samples by standard methods, including double precipitation of both t h e calcium oxalate and magnesium ammonium phosphate, and t h e titration of t h e acidified calcium oxalate with N/IOpotassium permanganate.
V O ~8,. NO.
I
TABLE II-PERCEXT.4GE
-hALYSES O F SAMPLES B Y S T A X D A R D X E T H O D S ASD B Y PROPOSED METHOD Results by standard methods Results by author's method(6) InsoLres. Insol. res. NO. a m m . p p t . CaC03 hZgcos TOTAL amm. ppt. CaCOs M X C O ~ 1 10.50 54.60 34.70 99.8 10.50 56.24 33.26 10.54 5 4 , 55 34.77 99.82 10.48 56.37 33.15 2 53.18 8.92 38.07 100. I , 8.90 50.61 40.44 8.95 53.24 38.00 8 86 100.19 50. i 5 40.29 3 63.00 3.25 33.90 100.15 3.95 58.73 38,05 3.22 63.04 33.84 100.10 3.24 58.61 38.15 4 66.82 3.94 29.39 100.15 3.95 64.69 31.36 3.97 66.90 29.25 3.97 100.12 64.66 31.37 5 59.19 3.24 37.63 100.06 3.24 5 6 , 2 8 40.48 59.19 3.30 37.66 3.20 100.09 56.34 40.36 6 49.02 11.40 39.60 100.02 11.36 49.06 39.58 11.36 49,05 100 04 39.63 11.30 49.12 39.58 7 50.85 11.32 37.65 99.80 11.30 54.06 35.64 50.82 37.il 11.33 99.86 11.33 53.88 34.79 8 49.70 39.76 10.20 99.66 10.15 53.28 36.57 49.74 39.72 10.16 99.62 10.18 53.09 36.73 9 68.85 4.20 26.95 4.18 99.86 70.04 25.78 68.79 4.25 26,96 99.90 4.15 69.95 25,90 10 2.10 92.28 5.62 100.07 2.12 94.71 3.17 22.36 2.04 5.60 100.02 2.08 94.75 3.12 11 ,7.25 22.65 99.90 22.70 77.22 0.08 77.22 22.71 22,64 77 35 99.93 0.01 12 6.33 92,85 100.07 6.31 2.80 92.79 6.36 6.41 100.01 90.85 2.74 13 91.32 99.94 8.62 8.74 90.25 1.01 91.26 8.66 99.92 8.72 90.28 1 .00 (a) N o t determined. ( h ) It is obvious t h a t in this method t h e total is always 100 per cent.
+
No. 1
10
11 12 13
+
TABLE 111-AVERAGES OF DUPLICATESIN TABLE I1 Insol, res. amm. ppt. Calcium Carbonate Magnesium Carbonate Standard Author's Standard Author's Standard Author's 10.52 10.49 54.57 56.31 8.93 8.88 53.21 50.68 3.23 3.23 63.02 58.67 3.95 3.96 66.86 64.68 3.27 59.19 56.31 3.22 11.38 49.09 49.03 11.32 50.83 11.33 53.97 11.32 10.18 53.19 49.72 10.16 4.16 4.23 70.00 68.82 2.07 94.73 2.10 92.32 22.68 77.29 22.67 77.23 6.36 6.35 90.87 92.82 9k.29 8.64 90.27 8.73
+
From t h e averages in Table I11 i t will be seen t h a t the combined weights of t h e insoluble residue and ammonia precipitate agree well within t h e limits of experimental error in both methods; t h a t in two cases (NOS. 6 and 11), the values for calcium carbonate are well within one per cent of each other; and t h a t in the remaining instances t h e deviation is about 2 or 3 per cent, varying from 1 . 0 2 per cent in No. 13, t o 4.35 per cent in S o . 3. As these variations represent both abnormally large and abnormally small differences, no constant could be used. SU31XfARY A N D C O N C L U S I O h 7 S FROXI S E R I E S I1
I-If the limit of inaccuracy for agricultural analysis is set a t one per cent. the proposed method, in its present state a t least, is hardly t o be recommended, b u t where only a n approximation is desired, it might be employed. 11-However, in t h e opinion of the writer, since t h e theory of the method does not appear t o be incorrect, there is required only a little further study of t h e experimental conditions involved t o make t h e method entirely applicable for agricultural purposes. 111-Three minor points of interest were developed during t h e investigation: ( I ) Ammonia precipitations may be made quantitatively in t h e cold, in t h e presence of ammonium salts, and with the aid of some macerated filter paper t o facilitate coagulation; ( 2 ) a half-normal hydrochloric acid solution may be heated, under t h e proper conditions, for 30 minutes or more on t h e water b a t h ( 8 6 ' ) , without loss of HCl; (3) ammonium chloride exerts a n inhibitory action upon the precipitation of calcium carbonate t o a much greater extent t h a n is generally ascribed t o it.
Jar
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
I n conclusion, the writer desires t o express his indebtedness t o Dr. F. E. Tuttle, head of t h e School of Chemistry, State University of Kentucky, not only for his general advice and suggestions during this investigation, b u t for his assistance in surmounting experimental difficulties t h a t at t h e time seemed insurmountable. CHEMICALLABORATORIES, STATE UNIVERSITYOF KENTUCKY LEXINGTON.KENTUCKY
THE PHENOL COEFFICIENT OF GERMICIDES’ By
FREDB. KILMER. A. WAYNB CLARK
AND
POWELL HAMPTON
The desire for a method of comparing t h e disinfecting or germ-killing power of disinfectants with some standard and of expressing t h e results i n definite figures is one of long standing. The “Rideal-Walker” and t h e “Lancet” methods have been a prolific source of discussion in England a n d in our country as well. The problem herein discussed is a n attempt t o show some of t h e experiences involved in a n attempt t o follow t h e so-called hygienic laboratory method a n d arrive a t results concurrent with t h a t of another laboratory. The problem is a t once trite a n d practical for t h e reason t h a t disinfecting preparations are a p t t o be examined in several laboratories under somewhat varying conditions with t h e consequent liability of discordant figures. T H E HYGIENIC LABORATORY METHOD
45
so t h a t notes and results could be compared in order t o arrive at a thoroughly satisfactory and safe conclusion. This work was done by t h e Lederle Laboratories of New York City, and will be referred t o later. CULTURE MEDIUM
A critical examination of t h e document containing the official method, with t h e object of proceeding with t h e work, immediately brought out t h e fact t h a t there was therein no positive statement as t o the formula of the culture medium used. This statement is made on t h a t subject: “Standard extract broth is used. . . .The broth is made from Liebig’s extract of beef and is in exact accordance with the standard methods adopted by the American Public Health Association for water analysis. It i s important that the reaction of the media is just +1.5.”
Careful reading of the above mentioned A. P. H. A. publication for 1912 shows it t o contain these statements: “Infusion of fresh lean meat, and not meat extract, shall be used as the basis of various media” and “the standard reaction of culture media shall be f 1 . 0 per cent.”
It is evident, therefore, t h a t there is no standard method for water analysis in which there is used broth made of beef extract or having a reaction of f 1 . 5 per cent. The reaction is, of course, easily adjusted b u t we call attention to t h e exceedingly loose statements made in this Bulletin, No. 82, and t h e consequent impossibility of complying accurately with its requirements on the information furnished. The formula for nutrient broth for water analysis given in the A. P. H. A. publication for 1912 is: Water . . . . . . . . . . . . . . . . . 1000 Meat . . . . . . . . . . . . . . . . . . . 500
Under date of April, 1912,there was published by t h e U. S. Public Health a n d Marine Hospital Service a pamphlet known as Hygienic Laboratory Bulletin No. 82. This contained a “Method of Standardizing Disinfectants,” b y John F. Anderson a n d Thomas 10 Peptone.. . . . . . . . . . . . . . . . B. McClintic. T h e method has since become known As ordinary broth is seldom used in water analysis as t h e “Hygienic Laboratory Method” according t o we examined t h e formulas for gelatin and agar media, the suggestion of t h e writers. I t has, we believe, been generally recognized t h a t this method has become these being the commonly used media. We find t h a t t h e official U. S. procedure for determining t h e value of gelatin t o be: Water . . . . . . . . . . . . . . . . . 1000 Meat . . . . . . . . . . . . . . . . . . . 500 of disinfectants. A casual examination of this publicaPeptone . . . . . . . . . . . . . . . . . 10 Gelatin . . . . . . . . . . . . . . . . 100 tion is sufficient t o indicate t h a t t h e subject has been thoroughly gone over a n d t h a t t h e older methods have and for agar: Water . . . . . . . . . . . . . 1000 M e a t . , . . . . . . . . . . . . . . . . . 500 received attention and criticism. The authors have 20 Agar . . . . . . . . . . . . . . 10 t o 15 Peptone. . . . . . . . . . . . . . . . . attempted t o retain the good points of each of these older methods a n d a t the same time t o improve a n d It is plainly evident, therefore, t h a t i t is impossible revise in those points which seemed to them to be open t o choose t h e formula intended, b u t as t h e agar fort o objection. On t h e whole, t h e points brought mula is t h e one used where t h e culture is incubated forward seem to be well taken and the improvements a t 3 7 ” C., it was decided t h a t t h a t one should be used t o be along the line of making t h e method more practi- for this work on disinfectants because t h e incubation cal, more easily carried out by t h e average operator, temperature is stated t o be a t t h a t figure. Also it iess liable t o variations due t o t h e personal equation, was thought t h a t t h e exactness of t h e formula of the a n d capable of being carried out without t h e use of broth was probably n o t ‘ a very important factor. How far wrong was this belief will be seen later. Note unusual or special apparatus. The testing laboratory of Johnson a n d Johnson has t h a t S A L T is not mentioned in any of these formulas, tried out t h e method thoroughly and applied i t t o and also t h a t in t h e 1905 edition of the A. P. H. A. those substances manufactured by Johnson a n d Johnson “Methods of Water Analysis” it says: “Sodium chloride shall not be added to any culture medium which lay claim t o germicidal properties. This being a new a n d not yet well-tried method, herein specified.” i t was determined beforehand t o have t h e results The amount of beef extract t o be used was presumed carefully checked by a n outside independent laboratory t o be 3 grams and our formula was: 1 Presented a t the 50th Meeting of the American Chemical Society, 1000 grams 3 grams W a t e r . , . . . . . . . . Liebig’s beef extract.. . New Orleans, March 31 t o April 3, 1915. Peptone (Witte) ....... 20 grams Reaction.. . . . . . . + 1 . 5 per cent
