Jan., 1916
T H E JOCRNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
T h e following results were obtained: PER CENTSUCROSE PRESENT ACTUALLY 33.40 40.00 43.60
PER CENT SUCROSE FOUND Polariscopic Gravimetric method method 33.25 33.20 40.24 39.99 43.51 43.56
M E T H OD
After removing t h e label, the can of condensed milk is heated for a short time in a 100' oven, cooled in a desiccator, weighed, t h e contents, weighing from 1 2 t o 1 5 ounces, transferred by'means of hot water and a suitable funnel to a 5 0 0 cc. volumetric flask. This may be accomplished most readily by punching two holes in opposite positions near t h e circumference of the top of t h e can, inverting the can over a funnel in a fixed position and allowing the can t o drain till practically empty, then removing t h e top and washing out the remainder. The empty can is then dried a n d weighed in t h e same manner as before a n d t h e weight of milk in t h e can ( W ) thus determined. The contents of t h e flask are shaken until all crystals of lactose and cane sugar are dissolved and the milk solution homogeneous; then t h e flask is filled t o t h e mark with water, cooled t o room temperature and shaken. Two aliquot portions of jo and IOO cc. measured in volumetric flasks, are transferred with rinsings t o zoo cc. volumetric flasks and clarified by t h e addition first of I . j cc. of 5 per cent phosphotungstic acid solution for each I O grams of condensed milk contained in the aliquot, and then after shaking, by t h e addition of 2 . 1 cc. of a 2 j per cent neutral lead acetate solution for each I O grams of condensed milk contained in t h e aliquot portion. The flasks are well shaken and then made up t o t h e mark, well shaken again, a n d filtered. To t h e filtrates measuring about 100 cc. are now added potassium oxalate crystals in portions of 0.1gram at a time, with constant shaking, until a curdy precipitate forms which quickly settles leaving a clear liquor. Usually 0 . j gram of the potassium oxalate is sufficient, a n d a large excess should be avoided. The solutions are again filtered, using a hardened filter containing 3 t o j grams Fuller's earth placed in the apex and testing t h e first I O cc. or so with more potassium oxalate crystals for complete removal of lead, a n d a portion of t h e filtrates polarized at 20' C., preferably on a Bates instrument set for maximum sensitiveness a n d using a bichromate cell. Multiplying t h e reading .of t h e dilute solution by 4 and subtracting t h e reading of t h e stronger solution from t h e product gives t h e direct polarization (P) of t h e solution corrected for t h e volume of precipitate. Two aliquot portions of 5 0 cc. of t h e filtrates are measured into I O O cc. flasks by means of pipettes; 5 cc. of concentrated HC1 (38.8 per cent) added t o each, and t h e resulting solutions allowed t o stand over night at room temperature. The room temperature should not be below 20' C., b u t preferably around 2 j ' C. I n t h e morning a few drops of phenolphthalein are added t o t h e solutions a n d they are then neutralized with strong NaOH solution. A few drops of N / I O HC1 are added t o dispel the pink color, t h e solutions are made up t o t h e mark, cooled t o room temperature
if necessary, and then polarized in the same manner as before inversion, preferably using 400 mm. polariscope tubes on other instruments t h a n those of t h e Bates type. The corrected invert polarization is obtained by subtracting the polarization of the strong solution from 4 times t h e polarization of t h e weaker solution, in t h e same manner as before inversion. Multiplying this corrected invert polarization by 2 , except where 400 mm. tubes have been used, gives (P') the invert polarization corresponding t o ( P )t h e polarization before inversion. Substituting these values in t h e following equation gives t h e per cent of sucrose in the condensed milk. 2 6 0 0 0 ( P - P') Per cent sucrose = W (141.7 - T / 2 ) Where W = weight of condensed milk contained in can and T = temperature in degrees centigrade at which invert reading is made. All flasks a n d pipettes used should be carefully standardized for true cubic centimeters at 20' C. U. S. CUSTOXS SERVICE PORT OF NEW Y O R K
THE DETERMINATION O F MOISTURE IN SYRUPS BY THE CALClUM CARBIDE METHOD By R. M. WEST Received June 4, 1915
INTRODUCTION
The determination of moisture in organic, as well as in inorganic, substances is a source of much difficulty. This is due largely t o t h e fact t h a t in many instances chemical changes, either increasing or decreasing t h e weight of t h e material, take place at t h e temperature necessary for t h e evaporation of t h e moisture and, in others, compounds are present which volatilize with t h e water during t h e determination. Attempts have been made t o correct for t h e errors inherent in t h e ordinary drying process by drying ( I ) i.n Z J U C U O , ( 2 ) in a n atmosphere of neutral gas, ( 3 ) at low temperatures over dehydrating agents, a n d (4) by distilling t h e moisture from large samples, together with oil, a n d measuring t h e water obtained. None of these modifications, however, are entirely satisfactory. Syrups, fruit juices, substances with a high fat content, a n d those containing other volatile compounds are particularly troublesome. The syrups, after concentration t o a point a t which only five or ten percent of the water remains, become so viscid as practically t o prevent further drying. The addition of sand or pumice, as prescribed by the A. 0. A. C. official method,' results more or less satisfactorily, depending upon t h e proportion used and t h e original moisture content of t h e syrup. Tables I and I1 show quite clearly t h e variation t o which results by this method are subject. Furthermore, t h e long continued heating t o which it is necessary t o subject a syrup in order t o arrive at nearly constant weight, results in some inversion of t h e sucrose, thus decreasing t h e apparent moisture content. This is especially marked when considerable amounts of acid 1 U. S. Department of Agriculture, Bureau of Chemistry, Bull. 107, (revised) 64-65.
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T H E J O U R N A L OF IiVDUSTRIAL A N D ENGINEERING CHEMISTRY
are present, t h e inversion varying with the acidity of t h e syrup and with t h e length of time required for drying. It is clear, too, t h a t attempts t o dry a syrup t o absolute constant weight must be unsuccessful, as t h e syrup will continue t o lose weight as long as t h e patience of t h e analyst will permit t h e experiment t o continue. A number of methods have been proposed a s substitutes for the official method and its modifications. One of these1 is t o treat t h e material t o be analyzed with a n alkyl magnesium halogen compound and measure the methane evolved. Another, first suggested in 1900 b y Danne,2 is t o treat similarly with calcium carbide and measure t h e acetylene either b y loss in weight or gasometrically. Danne originally proposed t h e method for t h e determination of moisture in substances containing other volatile constituents; DuprC3 reports success with t h e method when used for moisture in ammonium oxalate, cordite a n d similar substances containing volatile matters other t h a n mater; Cripps and Brown4 proposed using Danne’s method for moisture in spices and aromatic drugs; a n d from time t o time analysts; have reported t h e satisfactory extension of t h e method t o other substances. E X P E R I M E NT A L
Incidental t o a project on sorghum syrup, it soon appeared t h a t some method for moisture, more satisfactory and reliable t h a n t h e A. 0. A. C. official method, would have t o be adopted. This necessity was due, first, t o the fact t h a t t h e experiment included a moisture determination on so large a number of samples t h a t the time required for t h e repeated weighing and drying b y t h e official method was a n objectionable feature; a n d , s e c o d , because t h e plan of the work involved a comparison of t h e finished syrups with t h e respective raw and defecated juices from which they were made. This comparison could be made properly only on a n absolute dry matter basis, and previous experience with the official method had shown it t o be of doubtful value for such a purpose. Attempts were made, therefore, t o utilize t h e calcium carbide method. T h e experiment as conducted b y Danne, Dupre! and others, consisted in separating t h e carbide from t h e sample t o be analyzed with a layer of dry sand or wool and then, through heating t h e container, t h e moisture was driven off and in cont a c t with t h e layer of carbide. Many of t h e objections t o the official method, however, would be equally 1 T h . Zerewitinoff, “The Quantitative Determination of Water in Substances b y Means of Alkyl Magnesium Halogen Compounds,” 2. a n d Chem., 50 (1911), 680-91; abstr. C. A . , 6, 203. 2 Paper read before Society of Chemical Industry of Victoria, 1900; cf. also, Chem. E n g . , 6 (1912), 163-164. 8 Analyst, 30 (1905), 266-273; 31 (1906). 213-218. 1 Ibid., 34 (1909), 519-523. 6 R . W. Roberts and A. Fraser, “Easy Process for Estimating Water in Petroleum,” J . SOC.Chem. Ind., 23 (1910). 197; Irvine Masson, “ T h e Use of Calcium Carbide for Determining Moisture,” Chem. News, 103 (1910), 37-38; Irvine Masson, “ T h e Action of Water of Crystallization on Calcium Carbide,” J . Chem. Sot., 97 (1910), 851-867; A. C. D. Rivett, “ T h e Determination of Water in Butter,” Chem. News, 104 (1911), 261; Irving C. Allen a n d Walter A. Jacobs, “Method for t h e Determination of Water in Petroleum and I t s Products,” Orig. Com. 8th Inlev. Congr. App2. Chem., 10 (1912), 17-23; Korff-Petersen, “ T h e Use of Calcium Carbide in Estimating t h e Moisture in M o r t a r , ” Z . H y g . , 75, 236-44; abstr. C, A . , 7 (1913). 4056; F. H. Campbell, “ T h e Determination of Moisture in Organic Substances,” J . SOL.Chem. Ind.. 32 (1913). 67-70.
Vol. 8 , No.
I
valid as applied t o this, since the same factors which interfere with complete evaporation of the water would prevent the formation of acetylene equivalent t o t h e total amount of moisture originally present in the syrup. Roberts and Fraser,l Masson, Rivett and others had modified the original method t o the extent of mixing the carbide directly with t h e material under examination. An apparatus similar t o t h a t described b y McNeiP was tried and the details of the method as described b y him were followed. The addition of the carbide directly t o t h e syrup, however, refused t o give concordant results, due largely, as experience showed, t o the incomplete mixing of the two. Admixture of barium sulfate and silica, as proposed for liquids, was abandoned as failing t o give satisfactory results. This failure was judged t o be due t o loss of moisture b y evaporation while incorporating the inert materials, and t o the fact t h a t t h e local increase in temperature caused by the first addition of t h e carbide was sufficient t o fuse the particles of syrup-coated silica together, thus preventing a thorough mixing with t h e carbide. An a t t e m p t was made t o utilize some solvent which, containing little or no water itself, would leave t h e syrup in a liquid condition after t h e moisture had been removed as acetylene. The only solvents lending themselves t o such a use are alcohol, glycerine, and acetone. The alcohol was discarded, since in concentration sufficient t o eliminate excessive error due t o added mater, it was impossible t o obtain a homogeneous mixture with t h e syrup. With acetone, the solubility of acetylene is so high and so variable, with t h e changes in temperature t o which the apparatus is subjected? t h a t t h e errors introduced made t h e method not feasible. Glycerine, t h e most promising of t h e three solvents, apparently reacts with t h e carbide or t h e lime produced in the reaction, since a cons t a n t gas volume could not be obtained. 4 s a result of these experiments it was concluded t h a t no satisfactory method could be devised unless a thorough mixture could be obtained between the syrup and t h e carbide. Attempts t o determine t h e moisture b y loss in weight of acetylene, when the syrup and carbide were well stirred in a n open container, were equally unsuccessful, due t o loss in moisture driven off b y the heat of t h e reaction before it was acted upon b y the carbide. It became clear, t h e n , . t h a t some means of thoroughly mixing t h e carbide a n d the syrup within a closed container would have t o be devised, and since t h e measurement of loss in weight due t o t h e evolution of acetylene introduces a larger experimental error t h a n t h e measurement of t h e volume of t h e gas, it seemed preferable t o measure t h e gas volumetrically. DESCRIPTIOX O F APPARATUS
The diagram shows the apparatus t h a t was finally adopted for t h e determination. This is practically a modified alkalimeter and differs in principle from t h a t proposed b y McNeil ( I ) in t h e form of generating flask, t o which a stirring device has been added and See foot-note 5 in preceding column. “ T h e Calcium Carbide Method for Determining Moisture.” U. S. Dept. Agr., Bur. of Chem., 1912, Ciuc. 37, 1-8. 1
9
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T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
(2) in t h e introduction of a drying tube, containing calcium chloride, between t h e gas burette a n d t h e generating flask as protection against too high yields of acetylene, due t o the' action of t h e water vapor from the burette. A is a burette graduated t o contain 1 2 5 0 cc., enlarged a t t h e upper end t o a bulb, B , of approximately one liter capacity. The cylindrical
33
t h e rubber stopper 0 a n d is bent so as t o enable i t t o reach all points of t h e generator. The stopper is connected t o t h e neck of t h e flask by means of a heavywall rubber tube, P. The distance between t h e cork a n d t h e flask is 3 or 4 cm., and t h e flexible tubing permits t h e stirring rod t o be turned in all directions a n d thorough stirring a n d mixing of t h e contents of t h e flask, with neither t h e loss of acetylene nor increase in volume, due t o t h e admixture of air. Q serves as a container for t h e carbide previous t o mixing with t h e contents of t h e generating flask, and is fitted with a stopcock, R , which may be opened a n d closed immediately preceding t h e determination in order t o equalize t h e pressure within t h e generator. The t u b e K should be long enough t o permit sufficient distance between t h e burette a n d t h e water b a t h so t h a t t h e temperature of t h e gas will not be affected. The apparatus is not complicated and, with t h e exception of t h e burette A a n d t h e generating flask M with t h e bulb Q , can be assembled from such supplies as are usually t o be found in any laboratory storeroom. DETAILS O F T H E METHOD
APPARATUS FOR MOISTURE DETERMINATION BY CALCIUM CARBIDE METHOD
portion of t h e burette is graduated in 0 . 2 cc. a n d t h e scale reads from 1000 t o 1 2 5 0 cc. C is a tube of about t h e same bore as t h e burette by means of which a fairly constant pressure may be maintained in t h e burette throughout t h e determination. The smaller t u b e F , attached t o t h e burette b y means of flexible tubing, can be raised or lowered a t t h e conclusion of t h e determination, in order t o read t h e gas within t h e burette at atmospheric pressure. D is a reservoir connected through t h e outlet E , t o a water pressure p u m p and through t h e tube V t o t h e burette A a n d t h e tubes C a n d F . At t h e t o p of the burette is a three-way stopcock, G , leading through H t o t h e t u b e C a n d through I t o t h e drying tube J which is filled with calcium chloride. M is a flask in which t h e acetylene is generated; i t is connected t o t h e calcium chloride t u b e through t h e drying tube L containing calcium carbide, which serves t o convert t o acetylene t h e moisture driven off by t h e heat of t h e reaction. The stirring rod N is inserted part way into
The determination of moisture is carried out as follows: The generating flask M is weighed, from 5 t o I O grams of t h e sample introduced (if a syrup or other liquid, by means of a pipette), a n d t h e flask a n d contents reweighed. The bulb Q is filled with finely powdered calcium carbide, about 2 5 grams being used for each determination. This amount is a large excess over $hat actually required t o complete t h e reaction, b u t i t was found that t h e time required t o reach t h e end point of t h e reaction could be materially shortened b y using larger quantities. The stirring rod and calcium carbide bulb are attached t o t h e generator and t h e generator, in turn, t o t h e burette. These rubber connections are wired with copper wire for each determination, as t h e agitation t o which t h e flask is sdbjected together with t h e pressure occasionally caused b y t h e rapid generation of t h e acetylene, render t h e use of ground glass connections impracticable. The stop-cock a t the t o p OE t h e burette is opened into t h e tube C and t h e burette a n d tubes C and F are filled from t h e reservoir with water previously saturated with acetylene. This is done by opening t h e stopcocks S, T a n d U a n d forcing t h e water up t h e tubes by pressure from a water blast. The stop-cocks, except at G , are then closed. Pressure in t h e flask M is equalized by opening and closing pinch-cock R. The stop-cock G is turned so as t o open into t h e tube I . Communication between A and C is established by opening S, and t h e stop-cock T leading t o t h e reservoir of water is then opened so as t o allow t h e liquid in C t o recede about 2 0 or 2 5 cm. The apparatus is now ready for t h e moisture determination. The calcium carbide is gradually transferred from t h e bulb Q t o t h e generating flask a n d with each addition t h e mixture is thoroughly stirred. The water in C is kept slightly below t h e level in t h e burette so as to maintain t h e pressure as nearly constant as possible. It was found t h a t this precaution, while not absolutely necessary, is desirable in t h a t leaks through t h e rubber connections are less likely t o occur,
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T H E J O U R N A L O F IhTDUSTRIAL A N D E - V G I N E E R I N G C H E M I S T R Y
t h a n when such connections are subjected t o the pressure of the full column of water. During t h e addition of t h e calcium carbide, t h e flask should be immersed in cold water. This will prevent both the too rapid action of t h e carbide and temperatures so high as t o cause decomposition. Thorough and continuous stirring is necessary, not only for t h e proper mixing of t h e syrup, b u t t o prevent foaming into t h e outlet t u b e L . The mixture should become apparently d r y a n d fairly well broken up by the time half or tmothirds of t h e carbide has been added. T h e balance is then transferred rapidly t o t h e generating flask, stirred u p with t h e mixture contained there, and the flask with its contents is thoroughly shaken so as t o bring t h e fresh carbide in touch with all parts of the generator, Bask, stirring rod and connecting tubes. T h e carbide is t h u s given a n opportunity t o act upon a n y moisture which may have been driven off b y the heat of the earlier reaction and condensed upon t h e upper portions of t h e generating flask. The flask is then immersed in a water b a t h filled with a saturated solution of .sodium sulfate and t h e solution brought t o a boil. The mixture will boil at a few degrees above t h e boiling point of water. This temperature is maintained until t h e gas volume in the burette is constant for fifteen minutes. Experience has shown t h a t a volume constant for t h a t length of time does not further increase, except as it may vary due t o t h e variations in t h e temperature of the laboratory. As soon as t h e volume is constant, t h e generating flask is removed from t h e boiling water bath, immersed in cold water, and, after a few minutes, removed and exposed t o t h e air until a constant rolume of gas indicates t h a t the room temperature has been reached. The gas is then brought t o atmospheric pressure by means of t h e t u b e F and t h e volume recorded a n d reduced t o t h e corresponding volume for normal temperature and pressure. Several blank geterminations, using weighed amounts of recently boiled distilled water, gave results corresponding t o Duprk’s value for t h e water equivalent of t h e acetylene formed b y t h e reaction. This equivalent is o.oo1j2 j g. of Rater for each cc. of acetylene a n d differs from the theoretical value of 0.00162 g. due, according t o Dupr6, t o t h e retention of small amounts of moisture b y the hydrated lime formed during the reaction. McNeil suggests, on t h e other hand, t h a t this discrepancy may be due t o t h e presence of calcium oxide in t h e carbide. This latter explanation, however, does not appear tenable in view of t h e uniformity found in different lots of carbide. Until t h e cause for t h e variation is known, it is suggested t h a t a blank determination be made on each lot of carbide used. When the factor has been determined, multiply b y t h e corrected volume of gas t o obtain t h e equivalent weight of water, and the per cent of water in t h e original sample may then be calculated. COhIPARISOP; O F T H E R E S U L T S O F T H E C A L C I C 3 1 C.4RBIDE A K D A . 0. A . C. M E T H O D S
Table I shows a comparison of t h e results obtained by t h e calcium carbide method and t h e official method of t h e A. 0. A. C. as applied t o sorghum syrups. Six
Vol. 8, S o .
I
samples were selected for this comparison and determinations were made in duplicate b y each method. TABLEI-A COMPARISOA’OF RESULTSOF THE DETERMINATION OF MOISTURE IN SORGHUM SYRUPBY”THE CALCIUM CARBIDE AND A. 0. A. C. OFBICIALMETHODS Laboratory Calcium Carbide A. 0 . A. C. Official NO. I I1 AV. I I1 Av. 331f 34.6 34.7 34.4 35.4 35.0 35.2 3352 33.6 33.6 33.5 30.5 30.8 30.7 3328 29.9 26.4 29.7 30,l 26.9 26.7 3324 25.3 25.4 25.3 25.5 25.2 25.4 3329 20.1 20.1 20.3 20.2 20.0 20.2 3322 15.6 16.1 16.2 16.3 15.4 15.5
These samples were selected in order t o compare t h e methods as affected b y high and low moisture content and include two with t h e minimum amount of moisture, two with t h e maximum amount and two with a n average moisture content. The A. 0. A. C. method was followed exactly as prescribed, considering the end point t o be t h a t at which not more t h a n three milligrams loss was noted during a n hour’s drying. Examination of the table shows t h a t both methods are subject t o about the same variation between duplicate determinations, t h e average variation being slightly in favor OE t h e carbide method. The average of t h e determinations b y t h e calcium carbide method as compared with t h e corresponding averages b y the official method, show, with the exception of two of the samples, fairly concordant results. The variations of approximately three per cent in Samples 3 3 5 2 and 3 3 2 8 are evidence, however. t h a t t h e drying was incomplete although continued drying of these samples finally yielded results fairly comparable with those obtained by t h e carbide method (cf. Table 11). The drying of the samples was continued and in all cases with continued loss in weight indicating t h a t , n-hile the end point adopted b y t h e A. 0. A. C. is usually t h a t a t which the loss in weight is equiralent t o t h e moisture content of t h e syrup, there is no surety t h a t such will be t h e case. Furthermore, since it is not practical t o d r y t o constant weight, agreement between duplicate analyses may be deceiving as evidenced by t h e results obtained with Samples 3 3 52 and 3328. TABLE11-RESULTS OBTAINED B Y CONTIhUED DRYIA’GO F PORTIONS OF MOISTUREIN SYRUPS WEIGHEDOUT FOR THE DETERMINATION BY THE A 0. A. C. OFFICIALMETHOD
I
-
C
. Per GSiI
Lab. N ~ . 3317-1 3317-11 3352-1 3352-11 3328-1 3328-11 3324-1 332611 3329-1 3329-11 3322-1 3322-11
$
5,0610 5.1071 5.2061 5.2671 5.0093 5,1354 5 1104 5 2420 5.7053 5.17‘53 5,3344 5.6095
LI-ZE
$+”
cm 35.4 35.0 30.5 30.8 26.9 26.4 25.3 25.5 20.1 20.3 15.6 15.4
EX,-.-
p
26 27 28 28 28 28 26 26 29 27 26 26
cent moisture a f t e r additional drying of
20 hrs. 40 hrs. 60 hrs. 80 hrs. 36.4 36.8 37.1 36.1 36.7 36.3 37.1 35.8 34.0 34.4 33.4 32.7 34.2 34.9 33.5 32.8 28.6 29.0 28.1 27.6 28.4 28.8 28.0 27.6 27.0 27.3 26.5 26.1 27.7 28.2 27.0 26.6 22.8 23.6 22.1 21.5 22.9 23.5 22.3 21.5 17.6 17.2 16.6 16.3 17.8 17.4 16.8 16.3
APPLICATIOS O F T H E METHOD TO OTHER SUBSTAXCES
I n addition t o t h e work with sorghum t h e method was tried with butter a n d with fruit juices. I n t h e case of the butter, results were obtained in close agreement with those reported by Rivettl and i t is apparent C D Rivett, “ T h e Determination of Water in Butter,” Chem 1 A S e w s , 104 (1911), 261
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
t h a t in t h e case of such substances, high in f a t , t h e use of t h e stirring rod is of no additional value although equally well suited t o t h e determination. The principal advantage t o be gained by t h e carbide method is t h a t of a definite end point. I n drying fats, t h e increase in weight due t o oxidation may introduce serious error. With t h e calcium carbide method, t h e end point is very clearly defined, a n d it is reasonable t o suppose t h a t oxidation is prevented b y t h e atmosphere of acetylene with which t h e fat is in contact. On t h e other hand, i t should be borne in mind t h a t in t h e case of a fat containing free glycerine some error may be introduced by t h e interaction between t h e carbide a n d t h e glycerine. This same fact should be taken into consideration in applying t h e method t o soaps, containing glycerine. The official method is, of course, equally faulty in such cases, due t o t h e difficulty of drying glycerine a n d t o t h e fact t h a t glycerine slowly volatilizes at t h e temperatures employed. The method as applied t o fruit juices requires further A few facts regarding t h e determinainvestigation. tion are worth noting, however, a t t h e present time. The presence of acid in t h e fruit juice causes some hydrolysis on continued heating, thus decreasing t h e apparent moisture content if t h e latter is determined b y t h e official method. Furthermore t h e presence of volatile compounds, such as acetic acid and alcohol, is a factor tending to increase the apparent moisture content. I n t h e carbide method t h e acids are also a source of error in t h a t they react with calcium carbide t o produce a calcium salt and acetylene. Attempt t o neutralize t h e acid would be valueless as the reaction would result in t h e formation of water which would similarly increase t h e apparent moisture present. T h e carbide method has a n advantage over a n y method depending upon t h e evaporation of t h e moisture, however, in t h a t t h e error may be definitely determined in each case a n d corrected for. Since t h e increase in apparent moisture due t o t h e action of t h e acid on the carbide is proportional t o t h e hydrogen ion concentration, i t is necessary t o determine only t h e total acidity of t h e juice a n d correct t h e volume of acetylene accordingly. The presence of alcohol does not influence t h e results by t h e carbide method unless present in sufficient concentration t o materially affect t h e vapor pressure within t h e burette or t o dissolve appreciable quantities of acetylene. CONCLUSIONS
of solids in the syrup sample a n d sand on which t h e syrup is dried. IV-The carbide which is used should be subjected t o a blank determination t o determine t h e water equivalent. V-The method is especially adapted t o substances easily denatured at high temperatures a n d t o those which lose other volatile substances (not permanent gases) during t h e usual process of drying. VI-The method can be used when acids are present b y correcting t h e volume of acetylene for t h e total acidity. DIVISION OF AGRICULTURALCHEMISTRY DEPARTMENT OB AGRICULTURE,UNIVERSITY OF MINNESOTA ST. P A U L I MINNESOTA
ACID SOILS AND THE EFFECT OF ACID PHOSPHATE AND OTHER FERTILIZERS UPON THEM By S. D. CONNER Received August 2, 1915 INTRODUCTION
Soil acidity is of such complex and variable character t h a t soil investigators have not been able t o agree as t o its exact nature. For a long time i t was supposed t o be due entirely t o the presence of organic acids. Humic acid was t h e name given t o t h e first of these. Afterwards ulmic acid, crenic acid and apocrenic acid were discovered. It is now generally held t h a t t h e above-named acids are not definite chemical compounds, b u t probably represent groups of organic compounds of a more or less acid character. They are generally spoken of by recent writers as "humic or humus acids." I n recent years inorganic compounds of a n acid reaction have been recognized as important factors in soil acidity. I n regard t o mineral soil acidity there is great difference of opinion as t o whether i t is of a chemical or a physical nature. Among t h e numerous contributors t o t h e literature on t h e subject may be mentioned: Cameron,' Kohler12 Parker13 H a r r i ~ ,Wiegner,5 ~ Gans16 Van Bemmelen,' Sullivanls Veitch,g Loew,'O and Daikuhara." T H E EFFECT O F S O L U B L E S A L T S O N A C I D S O I L S
Practically all methods for quantitatively estimating soil acidity depend upon t h e reactivity which t h e soil may have with bases: either free or combined. The reason different soil acidity methods do not give accordant results is due t o t h e variable composition of soils a n d t o t h e fact t h a t t h e various acid constituents of soils show different degrees of reactivity with 1
I-The calcium carbide method for moisture is accurate within three- or four-tenths of a per cent a n d equal in this respect t o t h e present official method of t h e A. 0. A. C. 11-The proposed method is more satisfactory t h a n t h e official method inasmuch as t h e end Doint is clearlv defined, a n d t h e determination may be completed within a much shorter period of time. 111-The official method is open t o criticism because of t h e uncertainty of results where there has been variation in stirring or variation in t h e relative amounts
35
2
8
F. K. Cameron, "The Soil Solution," 1911, p. 66. E. Kohler, Ztschr. Prakt. Geol. Jahrg., 11 (1903), 49. E. G. Parker, U.S. Dept. of Agr.. Jour. Agr. Res., 1, No. 3 (1913). J, E. J . Phys, Chem,, No, (1914), 355,
G. Wiegner. JOUY. Landw., 60, NO. 2. p. 111; s ( i g i z ) , 197. R . Gans, Internat. Mitt. Bodenk., 8, No. 6 (1913), 529-571; Centbl. M i n . Geol. U. Pol., No. 22. p. 699; 23 (1913), 728, and No. 9, p. 273; 10 6 8
(1914), 299. 7 J. M. Van Bemmelen, Deul. Chem. Ges. Ber., 11 (1879), 2223; Landw.
v e r s ~ ~ s . ~ . ~ ~ ~ l ~ ~Sur,, , h 'Bull, , 8 ~313) . (1907). ~eol,
9 F. P. Veitch, J . A m . Chem. Soc.. 26 (19041, 637: see also Hopkins, Pettit and Knox, U. S. Dept. Agr., Bur. Chem., Bull. 78 (1903). , a n ~ ~ o ~ ~ ~ ~ ~ ~ , "Sta., ~ ~u.~ ~Dept. ~cp Agr., 6 1 E xl3 p(1913); t'
s.
11
G. Daikuhara, Bull. I m p . Cen. E w p f . Sta. Japan, No. 1 (1914), 1-4.
