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
where x = Per cent dextrose.
y = Per cent levulose
R = Reducing sugars as dextrose. P = Polarization of a sucrose normal weight on a saccharimeter, 200 S = Sucrose
c.
T h e d a t a obtained froni t h e investigation will be found in t h e accompanying table. I t will be noticed t h a t i n every instance t h e a m o u n t of levulose exceeds t h e combined amounts of t h e other sugars present, a n d though this work is b y no means exhaustive, i t b y so much substantiates t h e statements previously made t h a t levulose is t h e sugar predominating in apple juices. U. S. INTERNAL REVENUELABORATORY D. C. WASHINGTON,
THE INFLUENCE OF CALCITE INCLUSIONS ON THE DETERMINATION OF ORGANIC CARBON IN SOILS By EDMUND C. SHOREYA N D WM. H. FRY Received February 28, 1917
I t has been pointed out b y hlcCaughey a n d Fry1 a n d b y Robinson2 t h a t soils derived from limestones, especially those of t h e Limestone a n d Uplands Province, are peculiar i n containing inclusions of calcite a n d iron oxide in quartz. I n a recent mineralogical examination3 of a number of samples of Hagerstown silt loam, one of t h e i m p o r t a n t soil types of t h e Limestone a n d Uplands Province, t h e almost universal presence of calcite inclusions in quartz was again brought t o our a t t e n t i o n a n d some consideration has been given their significance. Quartz is among t h e most resistant soil minerals a n d i t is evident t h a t crystals of calcite inclosed i n q u a r t z , so long as such q u a r t z particles were intact, could have no agricultural significance. I n fact, such calcite Bureau of Soils, Bull. 91, 1913. Department of Agriculture, Bull. laa, 1914. a T h e identification of calcite inclosed in quartz in the soils examined was carried oiit in the manner usual in work with the petrographic microscope. The soil was mounted in an oil having a known refractive index, preferably very close to the index of quartz as this mineral is thereby rendered practically invisible when the analyzing nicol is removed from the microscope tube. When the nicols are crossed the calcite grains are readily “spotted” by their high interference colors. T h e work from t h a t point on is simply confirmatory. Rarely the calcite grains show crystallographic outlines and in these cases the index of the grain can be determined by rotating the stage until the grain disappears and comparing the actual index thus noted with the index calculated for a calcite grain having the same orientation as the grain under consideration. Thq two indices thus obtained should of course be identical. T h e chief difficulty in this procedure is t h a t often the interference figures of the quartz and calcite mutually clash, but with patience grains can be found showing the figures with sufficient clearness to enable the grain t o he roughly oriented. When all the conditions are favorable as outlined above, there is no doubt as to the identity of the grains under observation. I n other cases the extremely high interference colors practically settle the question, the only probable source of error being the confusion of calcite with dolomite, but so far as any analytical error introduced by the inclusions in quartz are concerned i t makes no difference whether they are calcite or dolomite. So far a s is known a t present there is no other method of determining roughly the quantity of a given mineral on a slide except actual count of sized material, or measurement of heterogeneous material, and in this latter case, as in rock sections, the material must he of uniform thickness. I n the case of inclusions such as those under consideration i t is obviously out of the question to apply either of the methods mentioned above, and consequently the quantity of the inclusion present cannot be stated in quantita. tive terms. 1
3
Vol. 9 , S o . 6
probably .would be a less likely source of soluble calcium in a soil t h a n t h e calcium-bearing silicates. T h e analytical significance of such calcite inclusions cannot, however, b e ignored, for there are several determinations commonly made b y agricultural chemists where their presence would introduce a n error. I n carbonate or‘carbon dioxide determination, where t h e carbon dioxide is set free from carbonates b y a stronger acid, it is evident t h a t a n y carbonate completely protected b y inclusion i n quartz would not be determined b y a n y of t h e methods now in use. Since, however, such calcite or carbonate has no immediate agricultural significance, this error may be ignored where t h e determination is made for t h e purpose of indicating proper agricultural practice. A m o n g t h e methods used t o determine approximately t h e organic m a t t e r in a soil is one t h a t depends on determining t h e total carbon a n d calculating this t o organic m a t t e r b y t h e use of a n empirical factor. Two methods are i n use for determination of t o t a l carbon: combustion in a current of oxygen with or without copper oxide; or, oxidation of t h e organic m a t t e r t o carbon dioxide b y some moist oxidizing reagent a n d determination of t h e carbon dioxide evol.i-ed b y one of t h e usual methods. I n both cases determination of carbon dioxide evolved from a n y carbonate present is made on a separate sample a n d t h e q u a n t i t y so obtained deducted from t h a t t o t a l obtained on combustion, t h e difference being s t a t e d as organic carbon. T h e first method, usually designated t h e cupric oxide method, is not subject t o much modification a n d is considered a n absolute method b y which others are t o be judged. On account of its tedious character, however, other methods, usually designated moist combustion methods, have been devised. These usually depend on t h e oxidizing effect of boiling concentrated sulfuric acid t o which potassium dichromate has been a d d e d ; a n d proposed modifications of t h i s method relate chiefly t o t h e method of determining t h e carbon dioxide a n d t h e design of t h e a p p a r a t u s used. I n determining t h e organic carbon i n a soil containing inclusions of calcite in quartz b y either of these methods, i t would seem from theoretical considerations t h a t in t h e case of t h e moist combustion method the carbon dioxide of included calcite would not be set free, while in t h e case of combustion with cupric oxide t h e high temperature would decompose t h e calcite, r u p t u r e t h e quartz grains a n d t h e carbon dioxide set free would be calculated as organic carbon, since i t would not appear i n t h e ordinary carbonate determination. Examination of 2 8 samples of Hagerstown silt loam for calcite inclusions disclosed their presence i n all samples b u t one. One of these, a sample from C h a t tooga County, Georgia, was selected as suitable f o r determining whether or not these theoretical considerations would be borne out i n practice. A sub-sample ground t o pass a sieve 80 meshes t o t h e inch, well mixed a n d dried a t I O j O C., was used througho u t , all results being s t a t e d as per cent of t h e dried soil. T h e following determinations were made: (11 Combustion with cupric oxide i n a current of oxygen;
June, 1917
T H E J O C R N A L O F I S D C S T R I d L A N D ENGILVEERI.VG C H E M I S T R Y
(2) combustion with concentrated sulfuric acid , t o which potassium dichromate had been a d d e d ; a n d (3) combustion of t h e residue after moist combustion with cupric oxide in a current of oxygen. Determination of t h e carbonate in t h e soil gave results less t h a n 0.01per cent carbon and this has been ignored as a negligible quantity. I t was originally proposed t o subject t h e residue from t h e treatment with sulfuric acid a n d dichromate after washing and drying t o combustion with cupric oxide, b u t i t was found ‘that this material h a d absorbed a considerable quantity of chromium compounds and gave so much sulfur trioxide on heating t h a t it was not possible t o obtain concordant results for carbon when treated. in this way, and in place another portion of soil was treated with sulfuric acid and potassium sulfate as in a Kjeldahl digestion, heated until all organic matter was destroyed and t h e residue perfectly white, washed, dried and n-eighed. The following results were obtained, all figures being t h e mean of three closely agreeing results. T h e figures obtained on combustion of t h e residue after treatment with sulfuric acid and potassium sulfate m-ere calculated t o original soil.
TOTAL CARBOF Per cent lIoist combustion., . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0.71 Cupric oxide combustion of residue from moist w m bustion, . . . . . . . . . . . . . . . 0.12 I n soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Cupric oxide combustion.. .........................
589
quartz grains proceeds slom4y, and if t h e combustion is stopped a t t h e end of t h e period usually adopted, calcite inclusions can still be found under t h e microscope a n d t h e material will give more carbon dioxide on further heating. Theoretically if the soil n-ere ground so fine t h a t all calcite inclusions were exposed t h e carbon dioxide of such calcite would appear in t h e preliminary carbon dioxide determination and no error would be introduced in t h e subsequent combustion b y t h e cupric oxide method, b u t it does seem possible t o accomplish this in practice. I t is evident t h a t t h e inclusions are exceedingly minute, for the carbon dioxide calculated t o carbon in t h e preliminary carbon dioxide deterniination was less t h a n 0.01per cent, while t h a t obtained from t h e calcite inclusions by cupric oxide combustion n-as 0 . 1 2 per cent, working with a soil ground t o pass a sieve of 80 meshes t o the inch. T h e residue from a moist combustion after washing and drying was ground t o pass a sieve 130 meshes t o t h e inch and then leached with hydrochloric acid, and after this treatment calcite inclusions were still abundant when examined under t h e microscope. I t is, of course, apparent t h a t in a n y coniparison of methods all determinations should be made on samples ground t o t h e same degree of fineness.
s.
L-. DEPARTMENT O F -kGRlCLXTcRE BVREACOF SOILS, ~V-ISHINGTOS
0.83 0.80
-~
.~
SULFATE It is seen from these figures t h a t there is a reasonably close agreement between t h e total carbon obtained b y By R . F. GARDIXERA X D EDMUND C. SHOREP direct cupric oxide combustion of t h e soil, and t h a t Received February 16, 1917 obtained b y adding together t h a t obtained on moist Muscovite, one of t h e micas, is a mineral frequently combustion a n d cupric oxide combustion of t h e resifound in t h e rocks from which soils are formed and is a due. commonly occurring mineral in soils. I n some soil It has been frequently noted that moist combustion series i t is one of the characteristic or predominating methods have given figures for total carbon i n minerals, for instance in a sample of Gloucester stony soils than those obtained with cupric oxicle, and with loam after mechanical separation t h e sands were found the idea that the latter was an absolute method, it has been held that the moist combustion method fie- t o contain j per cent of muscovite and t h e silt 30 per quently gives figures lower t h a n t h e actual amount. cent. I n the same way a Of Perm loam The results obtained indicate that if this discrepancy was found t o contain 6 per cent of muscovite in the sand is found in t h e case of soils containing calcite included and per cent in the ‘Onsidered One Of the most Muscovite is in quartz. t h e facts are quite t h e contrary so far as total stable of soil minerals. Clark says,* “Muscovite, organic carbon is concerned. under ordinary circumstances, is one of t h e least alterof soils containing calcite I n other lvords, i n the able of minerals. T h e feldspar of a granite may be inclusions, t h e carbon dioxide of such calcite will not appear in t h e ordinary carbon dioxide determination completely kaolinized while the embedded plates Of b u t will appear i n t h e cupric oxide combustion and mica retain their brilliancy unchanged*” AfcCaughey a n d F r y say,3 “The micas are persistent b e calculated t o organic carbon. This is not t h e case with the moist combustion method and it m,ould Seem minerals in soils and show b u t little evidence of alterafair t o assume t h a t in case of soils containing calcite tion, a fraying of t h e edges a t times being quite charinclusions the figures obtained for organic: carbdn by acteristic, If alteration of t h e micas has t a k e n place this method are nlore nearly t h e t r u e value t h a n those i t has not influenced their Optical properties* It mould appear t h a t micas are t h e most stable of t h e b y t h e cupric oxide method. potash minerals found in soils except microline.” It should be stated in this connection that in order Johnstone reports t h a t after suspension of mica for a to obtain all the carbon dioxide in combustion of such soils b y the cupric oxide method the heating must be year in water charged with carbon dioxide very little be discerned.’ prolonged much beyond t h e t i m e ordinarily t a k e n for 1 U. S. Dept. Agriculture, Bull. 122 (1914). t h e oxidation of t h e organic matter. It would seem 2 “The D a t a of Geochemistry,” U. S. Geol. Surz’ny, 616, 1916. t h a t t h e decomposition of t h e included calcite a n d t h e Bureau of soils, u, s, Dept, Agr,, Bull. Bi (1913!. escape of t h e carbon dioxide b y t h e rupture of t h e 4 Qiiarterl)’ J . Geol. Soc. London. 45 (1889).
THE
OF SoLUT1oNS OF ON MUSCOVITE
