1036
*
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
Vol.
11,
NO. I T
9 8 ’. It was, therefore, pyrocatechin, and pyrogallol sulfuric acid and filtered from the potassium sulfate, was evidently not formed by heating the raw material. which crystallized out on standing. The liquid was E F F E C T OF ACIDS-This was investigated by heat- almost neutralized with sodium bicarbonate, shaken ing 2 g. of the original polyphenol preparation with I O O out several times with ether, the ether evaporated, cc. of 2 per cent hydrochloric acid under reflux for and the residue redissolved in water. The product was 2 * / 2 hrs. in a vigorously boiling water bath. Upon further purified by precipitating with neutral lead cooling, a small quantity of a reddish precipitate acetate, decomposing the precipitate with hydrogen settled .out, which was filtered off. It dissolved rea’dily sulfide, filtering off the lead sulfide, and evaporating in cold alcohol, and was reprecipitated from the solution the solution. I n this way a mass of fine, silky needles by adding water acidulated with hydrochloric acid. was obtained, slightly tinged with brown. They were It was, therefore, a phlobaphene, no ellagic acid being soluble in water, alcohoi, and ether, but not in benzene. formed. The filtrate from the phlobaphene was shaken They gave all the characteristic reactions of protoout several times with ether, and the ether evaporated. catechuic acid described above, and the melting point A considerable residue remained which was insoluble was found t o be 194’. in benzene. It was taken up in water and the soluThe filtrate from the lead acetate precipitate was tion filtered. I t gave a precipitate with neutral freed from lead and then tested for phloroglucin, lead acetate, soluble in acetic acid. The filtrate from but none could be found. The test with pine wood and t h e lead precipitate gave no precipitate with lead hydrochloric acid produced a bluish green color, due subacetate. Ferric alum solution produced a pure evidently to some protocatechuic acid, w.hich had not green color, which, on addition of sodium bicarbonate, been precipitated by t h e lead acetate. first changed t o blue and then t o a beautiful purplish The original product resulting after t h e potash fusion, red. Ferrous sulfate in neutral solution gave a fine when acidified with sulfuric acid, developed a strong violet color. Silver nitrate solution was reduced on odor of acetic acid. A part of the liquid was, therefore, warming, and ammoniacal silver solut.ion in the cold. distilled with steam, and a silver salt prepared from the Pine wood moistened with hydrochloric acid was distillate. Evidently small quantities of a phenolic colored bluish green. These reactions show t h a t proto- substance had also distilled over, as part of the silver catechuic acid was formed, and not gallic acid. This nitrate added was reduced t o metallic silver. The was further confirmed by the fact t h a t the character- solution was heated, the metallic silver filtered off, istic reaction of gallic acid with lime water, white pre- and upon cooling, the silver salt crystallized out in cipitate quickly changing t o blue, could not be ob- the form of the characteristic nacreous laminae of tained. Instead, lime water produced a beautiful silver acetate. This salt was found t o contain 65.10 purple color, which was, however, not due t o pyrogallol, per cent of silver, against 64.63 per cent calculated. because it was quite permanent, while the similar It was, therefore, free from propionic acid or other color produced by pyrogallol quickly changes t o brown. homologues. The results obtained show t h a t the tannin of the We are unable t o say what this substance, produced in addition t o protocatechuic acid, consisted of. The sugar cane is a pyrocatechin, derivative, closely remelting point of the protocatechuic acid was 183 O , sembling the oak tannins investigated by Trimble.’ against 199’ for t h e pure substance. A larger and However, it is not precipitated by Stiasny’s reagent,2 purer sample of this acid was produced in the potash formaldehyde and hydrochloric acid. fusion described below. SUMMARY The acid solution remaining after treatment of the The polyphenol of t h e sugar cane giving a green tannin with hydrochloric acid and after extraction with color with ferric salts is not pyrocatechin. I t is a ether was neutralized with sodium carbonate, and true tannin, giving a precipitate with gelatin, and is, purified by precipitation with lead subacetate. The like the oak tannins, derived from pyrocatechin, not lead in the filtrate was removed with sulfuric acid, the from pyrogallol. H e a t alone produces pyrocatechin, excess acid neutralized with sodium carbonate, and the and no pyrogallol; dilute acids give .rise to a phloresulting liquid tested with Fehling’s solution. A baphene and protocatechuic acid, but not ellagic or precipitate of cuprous oxide was obtained which would gallic acids; potash fusiOn yields protocatechuic and point to the glucoside nature of the tannin. But in acetic acids, but no gallic acid or phloroglucin. the author’s opinion this is no positive proof, because LOUISIANA SUGAREXPERIMENT STATION glucose may be present in the form of an adsorption AUDUBONP A R K , N E W ORLEANS, LOUISIANA compound, and the glucoside nature of the tannin could only be definitely proven if t h e tannin were crystalline LOW TEMPERATURE-VACUUM FOOD DEHYDRATION and contained glucose in definite proportions. By K . GEORGE P A L K , EDWARD M . FRANKEL AND RALPH H. M C K E E ACTIOX O F PLxALI-This was tested by first boiling Received June 18, 1919 5 g. of the tannin for 2’/2 hrs. with I O O cc. potassium INTRODUCTION hydroxide solution, 1.2 sp. gr. The product obtained did not give any reaction for caffeic acid, with ferric I n connection with the work of the Division of Food salts or phloroglucin-hydrochloric acid. The alkaline a n d Nutrition, Medical Department, U. S. Army, solution was evaporated t o dryness in a copper beaker Major (later Lieutenant Colonel) John R. Murlin and then heated t o fusion. The resulting mass was 1 “The Tannins,’’ 2, p. 90. 9 Chem. Zcntr., 2 (1908). 1832. dissolved in water, the solution acidified with dilute
XOV.,
‘rg19
T H E J O U R N A L O F ~ I N D U S T R I A LA N D E N G I N E E R I N G C E E M I S T A Y
requested t h e study of methods for preserving meat as part of t h e investigation of meat spoilage which was being carried on. It soon developed t h a t dehydration processes offered the most promising outlook. At t h e time, special attention was paid t o meat, b u t t h e broader aspects of dehydration as applicable t o all food products were kept constantly in view. Two of t h e important problems of t h e then existing emergency with regard t o foods involved transportation and the safety factor of food handling, transportation, and storage. A satisfactory method of dehydration would help t o solve both problems, making shipping simple and inexpensive and spoilage insignificant. I t is not necessary at this time t o discuss the general importance of food dehydration processes, as Prof. S. C. Prescott has lately given an excellent presentation1 of this subject.
The commercial vacuum shelf dryer used was one permitting hot water or low-pressure (sub-atmospheric) steam t o circulate through t h e shelves. The meat or material to be dried was placed on galvanized iron wire-gauze trays which could readily be run into t h e dryer onto t h e shelves and which gave metallic conduction from the heating surface t o the substance t o be dried. At the same time, t h e gauze trays carrying t h e material being dehydrated permit of evaporation of the water downwards as well as upwards. Such trays also can be readily cleaned. D E H Y D R A T I O N OF M E A T
The method of dehydrating meat is as follows: The ’bones and most of the fat are removed a t the time of slaughtering the animal, t h e meat cut into pieces of suitable size (cubes, steak or hash) and introduced into the vacuum dryer. If the dehydrating plant and the slaughter house are within a short distance of each PRINCIPLES I N V O L V E D other, the living animal heat can be retained in t h e I n t h e dehydration of meat, the following seem t o meat. The vacuum pump is started and a t the same be t h e important factors: ( I ) The temperature of time the hot water or low-pressure steam is circulated dehydration must be kept below the point a t which through the shelves. The process is interrupted from the proteins coagulate, and t h e fats melt; ( 2 ) with time t o time and the trays containing the meat retoo low a temperature the process of dehydration will moved, weighed, and the loss of water controlled. be unnecessarily prolonged with t h e result t h a t often The vacuum t o be maintained corresponds t o a pressure spoilage will occur and t h e overhead cost will be of about 2 in. of mercury. It is not necessary t o have greatly increased; (3) if the removal of water takes the dryer closed off entirely, b u t a “cracked” vacuum place exclusively from t h e outer surface, a s i n t h e use in which a small current of air is allowed t o pass of a stream of heated air, a cornified layer is likely t o through the dryer is permissible and sometimes deform, thereby preventing evaporation of moisture sirable, although the pressure must not be allowed t o from t h e inner parts and resulting ultimately in spoilage rise above t h a t indicated. The temperature of t h e of t h e product; (4) the fats in the meat must not be circulating fluid is kept a t about 70’ C. At first, when allowed t o become rancid as by oxidation; ( 5 ) a SUE- the meat contains most water and is most sensitive cient quantity of heat must be supplied t o evaporate the t o changes due t o heat and other causes, i t is probable large percentage of water present. Briefly, t h e condi- t h a t its temperature does not rise above 50’ because tions t o be met include a suitable temperature, ab- of the large amount of water being evaporated. A s sence of air, and t h e addition of t h e needed calories of the ineat becomes more dehydrated, and the rate of heat energy. evaporation of the water decreases, the meat becomes These conditions were first worked out with a small correspondingly warmer, until toward the end, when sized vacuum chamber, suitably modified, loaned by danger of decomposition by heat is least, the temperaProfessors H. C. Sherman and T. B. Freas, of Co- ture approaches t h a t of the shelves. lumbia University. The process was then carried The time of dehydration will vary with the size of over t o t h e commercial size vacuum dryer in t h e the individual pieces of meat used. With steaks chemical engineering laboratories of Columbia Uni- l / 4 in. thick, dehydration has been completed in 2 t o versity.2 3 hrs. There is not much difference in the time for The solution of the problem involves heating t h e pieces of stew size and ground for hash for t h e same meat (or other food product) cut in pieces of suitable quantities per square foot of pan surface. Stew-size size t o a temperature below t h a t a t which cooking or pieces after dehydration can readily be ground t o the appreciable changes in t h e meat take place; con- hash form by passage through a suitable meat grinder. Beef contains on the average 7 5 per cent of its tinuously maintaining a degree of vacuum such t h a t weight as water. With a shelf dryer having about 50 t h e vapor pressure of water a t t h e temperature employed is greater than the pressure within the vacuum sq. f t . of pan surface and holding I O O Ibs. of meat cut dryer, thus causing boiling and evaporation of t h e in pieces of stew size (I in. cubes), working as indicated, water from t h e inner parts of the meat as well as from t h e loss of weight in a n 8-hr. run was in the neighbort h e surface; and introducing a sufficient quantity of hood of 6 5 per cent. The most rapid loss in weight heat t o enable t h e large amount of water t o be evap- occurred during t h e first third of the time. A furorated by taking up the.requisite number of calories ther loss in weight can be brought about by additional of heat energy t o overcome the latent heat of vaporiza- time in the vacuum dryer, b u t a more economical method of working is possible. Beef which has lost tion of water. about two-thirds of its weight in water, when exposed 1 “Rc>lationof Dehydration to Agriculture,” U. S. Dept. Agr., Czrcular t o the atmosphere does not take up water again, b u t 126, January 25, 1919. on the contrary loses additional water and becomes * U S. Patent 1,309,357 of July 1919, and foreign patents.
1038
,
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
dehydrated further. By exposing the dehydrated meat from the vacuum dryer t o the atmosphere for two or three days, further decrease in weight takes place until the meat weighs in the neighborhood of 28 per cent of its original weight. Under these conditions i t contains approximately I O per cent of its final weight as water. Certain precautions must be exercised with regard t o this supplemental air-drying. If the meat is not dehydrated sufficiently in the vacuum dryer, in the process of air-drying a dry mold may appear on some of the pieces. This mold is harmless a n d does not spread after the meat is dehydrated satisfactorily, but i t does not look well and can readily be completely avoided by paying attention t o the first, main part of the dehydration. PROPERTIES O F DEHYDRATED MEAT
The dehydrated beef in stew size or as steaks is reddish brown t o brown in color. I t s volume is about one-half of t h a t of the fresh beef. After grinding t o hash form, the product is grayish brown in color. I t can be compressed readily t o smaller bulk. Exposed t o ordinary atmospheric conditions for a year no perceptible change occurred. I n a closed container saturated completely with water vapor, moisture was taken up very gradually and after four or five days a t room temperatures molds began t o appear on the meat. If the meat were taken out of the container a t any time before the molds appeared and exposed t o the atmosphere, reversion t o the original dehydrated condition occurred. I t is important t o mention t h a t the f a t in the meat did not turn rancid on keeping under ordinary conditions. TABLEI-ANALYSBS
MEAT BEFORE AND AFTER DEHYDRATION Dehy- -Dehydrated Meat, May 9Fresh drated IncuIncuMeat Meat Room Room bator bator Apr. 18 Apr. 20 Exposed Jar Exposed Jar Per cent of Meat . . . . . 9.83 9.87 10.4 9.92 Total nitrogen'. . . . . . . . 3 . 2 6 0.053 0.062 0.055 0 . 0 1 6 0.045 0.045 NH3 nitrogen'. 1.115 1.095 I . 139 1.056 0 . 3 2 9 0.975 N.P.N 1.042 1.095 1.008 1.074 N. P. N . minus NHs-N 0.309 0.919 0.044 0.053 0.048 0.041 0.020 0 . 0 5 6 NHs nitrogen.. 0.358 0.364 0.360 0.360 0.124 0.360 KI KeS nitrogen. 0,080 0.082 0.077 0.022 0.064 0.080 Purine nitrogen.. 0.570 0.605 0.655 0 . 1 6 3 0.495 0.628 Residual N. P. N . . Per cent of Total Nitrogen . . . . . 0.54 0.56 0.43 0.63 NHanitrogen'. . . . . . . . 0 . 4 9 10.7 10.7 11.0 11.6 N . P . N.............. 10.1 . . . . . 0.45 0.49 0.40 0.53 NHanitrogen . . . . . . . . . 0 . 6 1 3.62 . . , . . 3.66 3.62 3.50 Ki Keenitrogen ..,.. 3 . 8 . . . . . 0.82 0.81 0.79 0.78 Purinenitrogen,.. . . . . 0 . 6 6 57.7 60.4 61.0 . . . . . 66.6 ResidualN. P . N...... 50.0 1 Determined directly on meat; results not marked are on N. P. N. Filtrate. 2 KI f Kz = creatine plus creatinine. OF
....... ..............
+
....... .... ..... ...
.....
+
The dehydrated meat contained on the average per cent of its weight as moisture. Chemical analyses of the meat before dehydration, immediately after dehydration, and a t intervals thereafter up to four months were made. The constituents determined included ammonia, non.-protein nitrogen, creatine plus creatinine, and purines. The methods used have been described in detail e1sewhere.l The only additional points which need be mentioned are t h a t the sample was obtained as uniform as possible by carefully grinding and mixing, and t h a t for each analysis 7 0 g. were used, soaked in water for half an hour, and IO
1 K. G. Falk, E. J. Baumann and G. McGuire, J. Bid. Chem., 57 (1919), 525. For purine method, cf. also I. Greenwald. J . Biol. Chem., 85 (1916), 224.
Vol.
11,
No.
11
then treated in the customary way. The results are given in Tables I and 11. These experiments were carried out by Miss Grace McGuire and Dr. Emil J. Baumann. Table I shows the results of one series of experiments. The chilled fresh beef (48 hrs. after slaughtering) was analyzed April 18, dehydrated, and the dehydrated meat analyzed April 20. I t was then ground t o a powder, divided into four portions, kept under different conditions and analyzed again May 9, after 19 days. Two portions were kept a t room temperature (15-20' C.), one exposed t o the air, the other in a tightly closed jar; and two portions were kept similarly a t incubator temperature (3 7 O C . ) , The results show t h a t the meat was dehydrated t o about one-third of its original weight. After dehydration there was very little change. The part of the table in which results are given as percentages of total nitrogen brings this out more satisfactorily. The constancy of the ammonia results is noteworthy, as any decomposition would greatly increase the ammonia content. Table I1 gives the results over a longer period of time. The four different ways of keeping the dehydrated meat were the same as before. The results in this table show the composition of the fresh meat, of the meat immediately after dehydration, and after standing 1 2 , 3 2 , and 1 2 1 days under the different conditions. The appearance of the meat kept a t the ordinary temperature was unchanged after the four months. I n the incubator a t 3 7 O in this length of time, the meat took on a slightly cooked appearance. There was no odor of any sort noticeable a n d no signs of the growth of molds or bacteria. The chemical analyses show no essential change in the meat when the difficulty of accurate sampling is taken into account. Whatever slight changes appear t o occur are apparently negligible and cannot be expected t o change the properties of the meat. This is evident especially when comparing these results with the results obtained with meat undergoing decomposition, as, for example, in the ammonia content.' Several series of bacteriological tests were carried out with the dehydrated meat by Dr. F. HultonFrankel. One gram samples of the meat were carefully washed with ether t o remove surface contamination, placed in sterile saline solution over night in the incubator, and the saline extract cultured on agar plates. No organisms were found in several series of experiments. The dehydrated meat after removal of surface contamination is therefore sterile. The rate of taking up of water by the dehydrated meat preliminary t o its preparation for use depends t o a great extent upon its state of division. A large number of recipes have been developed but i t will be necessary t o give only some of the general principles here. With the hash form, enough water t o form a paste is added, the mixture allowed t o stand for I O min., and then prepared as when using fresh meat. The pieces of stew size or the steaks must be 1
K G. Falk and G. McGuire, J. B i d . Chem., 3'1 (1919), 547.
Nov., 1919
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
I039
-
TABLE 11-ANALYSES OF DEHYDRATED MEAT AT VARYINGINTERVALS AND CONDITIONS r Dehydrated Meat Room Exposed Room Jar Incubator Exposed Mar. 4 Mar. 24 June 21 Mar. 4 Mar. 24 June 21 Mar. 4 Mar, 24 June 21 Per cent of Meat 9.60 11.0 12.2 9.79 10.25 11.7 9.87 12.2 11.0 10.11 Total nitrogenl.. . . . . . . . . . 3 . 5 2 0.043 0.045 0 . 0 3 2 0.047 0.051 0 . 0 5 0 0.055 0.056 0.090 0.047 NHa nitrogen'. . . . . . 0.010 0.894 1.395 1.405 1.085 1.500 1.345 1.010 1.685 1.372 1.075 N. P . N 0.288 0.033 0.021 0 . 0 7 4 0.042 0.022 0.026 0.042 0.049 0.042 0.054 NHs nitrogen.. . . . . . . 0.01 1 0.46 0.48 0.40 KI &a nitrogen.. . . . . 0.40 0.51 0.388 0.51 0.39 0.37 0.13 0.44 0.077 0.078 0.081 0.079 0 . 0 8 4 0 . 0 7 9 0.072 0.083 0.084 0.074 Purine nitrogen.. . 0.017 0.419 0.837 0 . 7 7 3 0.561 0.955 0.725 0 . 5 1 6 1.057 0 . 7 3 6 0 . 5 5 4 Residual N . P. N . . 0.130 Per cent Total Nitroeen 0.26 0.48 0.49 0.43 0.56 0.46 0.45 0.41 0.82 0.46 NHa nitrogenl.. . . . . . . . . , 0 . 2 8 10.3 16.5 11.8 10.9 9.32 13.6 11.0 11.3 13.2 10.7 N.P.N. 8.19 KI I W nitrogen.. , 3.7 3.9 4.0 4.2 3.87 3.9 4.4 3.93 3.8 4.4 3.96 0.69 0.756 0.77 0.72 0.801 0.75 0.75 0.63 0.71 Purine nitrogen.. . . , 0.48 0.800 5.95 5.27 10.3 6.29 5.61 6.86 4.36 8.68 7.03 5.55 Residual N . P. R . . . , . 3.69 0 . 3 4 0 . 2 0 0 . 2 1 0 . 4 3 0 . 4 8 0 . 3 6 0 . 5 4 Ammonia nitrogen.. . 0 . 3 1 0 . 1 7 2 0 . 6 7 0.41 1 Determinations made directly upon meat extract; results not so marked determined on non-protein nitrogen filtrates. 2 KI Ka = creatine plus creatinine.
Fresh Feb. 20
Dehydrated Feb. 21
. . . .. . . . ................... . . . . . .. .. + . ....... .. .. .. .. .. . . + ................. . . .. . ........ .. ... . . .. . .
Incubator Jar Mar. 4 Mar. 24.June 21 ..
11.0 10.7 10.00 0.083 0.055 0 . 0 5 8 1.430 1.178 1.010 0 . 0 7 4 0.045 0 . 0 5 8 0.42 0.45 0.39 0.078 0.079 0 . 0 8 2 0.858 0 . 6 0 4 0 . 4 8 2 0.75 13.0 3.8 0.71 5.32 0.67
0.51 11.0 4.2 0.74 5.64 0.42
0.58 10.1 3.9 0.08 4.82 0.575
+
treated with water for longer periods of time, 8 t o 1 2 hrs. I n general, times of cooking should be slightly longer t h a n with fresh meat. The dehydrated meat has been used by a number of individuals, by the dietitians of several hospitals, and in an army camp. About 500 lbs. were shipped t o Asia Minor for the American Committee for Relief in the Near East, and another considerable shipment has just been dehydrated for use in a South American exploration expedition. DEHYDRATION OF FISH
The dehydration of fish is carried out in the same way as the dehydration of beef. The fish is either split and the bones removed, or steaks or slices cut. The product is satisfactory in every respect. Dehydrated salmon retains its color and flavor unchanged. Oysters and clams were also dehydrated without difficulty by the new process. D E H Y D RAT1 0 N 0 F VE GET A B LE S
The new vacuum dehydration process has also been applied t o a large variety of vegetables. The method of carrying out the dehydration was the same as with meat, except t h a t in a number of instances the time required was considerably less. The appearance of the products was satisfactory in every case. Chemical analyses of the products (nitrogen and ash determinations) show no facts of interest. The moisture content varied from 5 t o 2 0 per cent, depending upon the vegetable and length of time of dehydsation. With potatoes the procedure is as follows: No preliminary cooking or steaming is necessary. The potatoes are peeled, sliced into cold water, and then placed on the trays. Slicing into water keeps them from turning dark before putting them into the dryer. The dehydrated product is white in color and remains so.
Enzyme studies were carried out on vegetables dehydrated by the vacuum and air-blast processes and compared with the enzyme content of the fresh vegetables.' I n general, vacuum dehydration caused considerably less destruction of enzyme action t h a n did the air-blast dehydration. The physiologic actions of some of these dehydrated products are being studied b y Dr. Maurice H. Givens, of the University of Rochester, and by Dr. K. Sugiura, 1
229.
K . G. Falk, G. McGuire and E. Blount, J B i d . Chem., 88 (1919),
of the General Memorial Hospital, New York, by the former in connection with the antiscorbutic property toward guinea pigs, b y the latter in connection with the growth hormone toward rats. Their results will be communicated later elsewhere DEHYDRATION OF FRUITS
Very little need be added in connection with the dehydration of fruits by the vacuum process. Of special interest is the fact t h a t some can be dehydrated t o form white products, for example, apples, without treatment with sulfur dioxide. The method is excellent for the drying of coconut for the production of copra. No marked loss of flavor is noted in vacuumdried fruits. It would seem t h a t the low temperatures used prevent the volatilization of the essential oils so t h a t on rehydration the frnit has its original flavor. ADVANTAGES
O F T H E N E W PROCESS
The advantages in food preservation, including the obvious saving of space, weight, and refrigeration, are indicated in Prof. S. C. Prescott's publication already referred to. The specific advantages of the new vacuum dehydration process as compared with t h e hitherto used method of dehydration by means of a current of heated air may be mentioned briefly as follows: I-More economical operation. Only one-fourth of the fuel required by the heated air method. 2-Shorter time required, hence permitting products sensitive t o spoilage t o be handled. 3-Applicability t o such products as meat and fish. 4-Smaller chemical changes produced, e. g., fats not becoming rancid, etc. 5-In general, a more satisfactory character of product. Unoxidized, structure open (permitting ready hydration), less change in enzymes and hormones, and in case of fruits sulfur dioxide treatment not required t o keep original color. A disadvantage of the process is the initial cost of the apparatus. This cost is several times t h a t of the apparatus used when drying is carried out with a current of hot air. The interest on plant investment in any dehydration process is. however, a very minor part of the cost of operation. A C K N 0 W LED G ME NT
I n conclusion the writers wish t o express their thanks t o those who have aided them in various ways t o
I040
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY y t o Mr. Herbert f the experimental t o this investiga-
tion. HARRIMAN R E S E A R CLABORATORY ~ NEW YORKCITY RoOSSVBLT HOSPITAL,’ OB CUEMICAL ENGINEERING DI$PA~TML$NT COLUMBIAUNIVERSITY. Nsw YORK CITY
SOIL ACIDITY-THE RESULTANT OF CHEMICAL PHENOMENA’ B y H. A NOYES Received March 31, 1919
T h a t condition of soils known as acid is not confined t o any one soil type. The major portion of the soils of the-eastern half of the United States are acid in the sense t h a t they will grow better crops when treated with agricultural lime. Many of these soils were acid in their virgin state and the majority have or are becoming more acid through the loss of metals in drainage waters and crops. The number of years required t o bring about a n acid condition varies with t h e soil. The composition, origin, natural fertility, system of cropping, and cultural practices followed all bear on the acidity. Nitrogen, phosphorus, and potassium have been the three elements considered essential in fertilization practices. Calcium (in agricultural lime), though not usually classed as a plant food, is occupying as important a place in soil fertility investigations as either nitrogen or potassium. In an article entitled “Carbonic Acid Gas in Relation t o Soil Acidity Changes,” the writer made t h e following statement: “The changed reactions of this soil toward a neutral salt of a strong base and a strong acid (KNOI) after subjection t o the varied conditions of the experiments a t least suggests t h a t soil acidity is largely the result of hydrolytic mass action phenomena.” The present paper gives some of the reactions between water a n d soil constituents in relation t o soil acidity results and additional experimental d a t a in support of t h e statement just quoted. Investigators have looked t o the following substances and phenomena for the explanation of soil acidity: the presence of mineral acids, the presence of organic acids, free hydrogen ions, colloidal material, absorption and adsorption, and the presence of specific compounds. The methods used and in use for making soil acidity determinations are many. The methods include the treatment of soils with substances of both low and high solubilities. Salts of strong acids and strong bases, of strong 1 The experimental work covered by this paper was done while the author was employed as research associate in chemistry and bacteriology a t the Purdue University Agricultural Experiment Station. The author wishes to make acknowledgment to Mt. Lester Yoder for assistance in laboratory work, as well as t o Dr. C. A. Peters, of the Massachusetts Agricultural College, Mr. W. H. Beal, Chief of Publications, State Relations Service, and Mr. W. A. Hamor, Assistant Director of the Mellon Institute of Industrial Research, for criticisms and suggestions In the preparation of the manuscript.
Vol.
11,
No.
II
acids and weak bases, of weak acids and strong bases, of weak acids and weak bases, calcium hydroxide, t h e lowering of the freezing point of the soil, the catalysis of esters, and the hydrogen ion concentration have all been used in studying soil acidity. The results obtained by different methods have differed so widely with the same sample of soil t h a t statements similar t o the following are quite common: “Calcium acetate results are mainly due t o ‘organic’ acidity, potassium nitrate results give mainly the ‘inorganic’ acidity, and the Veitch lime-water method gives the calcium-fixing power of the soil.” To point out some of the reasons for variations in results obtained by the different methods and t o show the method of attack used in carrying out t h e investigations reported in this paper, the constitution of soils is considered in connection with some of the fundamental teachings of physical chemistry. The condition of a soil, a t any time, can be considered as a stage in its progress towards a constantly changing equilibrium in accordance with the principle of Le Chatelier Metals enter into reactions dependent on their places in t h e electromotive series, each one replacing (until a n equilibrium is reached) any one occurring later in the series. The order of the metals in the electromotive series is potassiwn, sodium, barium, strontium, calcium, magfiesium, alumilzum, manganese, zinc, chromium, cadmium, iron, cobalt, nickel, tin, etc. Those italicized are present in arable soils and stand well up in the series. To avoid a rather common misconception, i t must be noted t h a t the electromotive series cannot be used t o explain the tendency of one radical t o dislodge another in double decompositions. The influences which determine decomposition are the solubilities and ionizations of the compounds concerned. The law of mass action states t h a t the velocity of a chemical reaction is proportional t o the masses of the substances reacting, or, in other words, is equal t o t h e product of the masses of the reacting substances times a constant. This means t h a t where t h e constituents of a slightly ionized substance are present, t h a t substance will form a t the expense of other substances t h a t are more highly ionized. Table I gives the solubilities of some of the salts of those metals regularly found in soils and shows t h a t the inorganic sodium and potassium compounds t h a t occur in soil are all more or less soluble, t h a t calcium, magnesium, and manganese compounds are less soluble, and t h a t iron and aluminum compounds are still less soluble.
.
The ionization theory makes i t necessary t o consider t h a t chemical reactions take place between ions. If a sufficient quantity of any compound found in soils is put by itself with water and no reactions take place between ;t and t h e distilled water, there are present a t equilibrium the following ions from the salt, the dissolved salt, and the crystalline undissolved salt. This condition is dependent on the laws of chemical and physical equilibrium and can be illustrated by sodium nitrate.
