July, 1919
T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
637
A sample of Merck's urea gave 2 0 . 2 8 per cent carbon against a calculated 19.gg per cent, while sucrose gave 41.98 per cent against a calculated 4 2 . 0 8 per cent. It is probable, as has already been noted by Salter,* t h a t any oxides of nitrogen which may be formed are reduced in t h e zinc t u b e and hence are not a source of error in t h e determination. SUMMARY
A simple, inexpensive apparatus is here reported for t h e determination of carbon in soils and similar substances by t h e wet combustion method, using chromic and sulfuric acids. The total time for t h e determination is about 25 min. D a t a have been presented showing t h a t t h e method as outlined is subject t o errors of small magnitude. DIVISIONOF SOIL CHEMISTRY AND BACTERIOLOGY EXPERIMENT STATION AGRICULTURAL BERKELEY,CALIFORNIA
fir+?€
FIG 2-EFFECT
OF
/N DAYS
E X P O S UON R ~RAWLINSEEDOIL
1 0.95 Sq. Cm. Surface per Gram 011 11 = 2.00 Sq. Cm. Surface per Gram Oil E
vestigators. Ballantynel allowed linseed oil t o stand in an uncorked bottle exposed t o light. The oil was shaken daily and a t intervals analyzed. Ballantyne found t h a t under these conditions t h e iodine number decreased, while t h e specific gravity and acid number increased without a change in volume. Sherman and FalkZ studied t h e same question similarly and found a lower iodine number and higher specific gravity and a small increase in acidity. These authors found a 3.43 per cent increase in specific gravity calculated on t h e original weight, while elementary analysis showed t h a t t h e oil had taken u p 3.16 per cent oxygen. They concluded t h a t the greater increase in specific gravity was probably due t o a slight contraction in volume. Sabin3 exposed raw linseed oil in thin films for 8 mo. and found a specific gravity of 1.098 and a gain in weight of not more t h a n 2 per cent. Assuming a specific gravity of 0.932 for t h e original oil, Friend4 calculated a contraction in volume of 13.4 per cent for Sabin's film. Thompson6 exposed two varieties of raw linseed oil in thin films for 2 1 2 days and found .
. ...
North American Oil. South American Oil., .
h E ' / N DAYS
Fro. 1
The changes which take place in linseed oil when exposed t o air have been studied b y a number of in1
THIS JOURNAL, 8 (1916), 637.
Sp. Gr. . 1.16 1 . 15
Gain in W t . Per cent 8.25 7.70
Decrease in Vol. Per cent 13.0
12.4
Friend6 oxidized raw Calcutta oil by passing air through t h e oil and by spreading in thin films on glass. He found t h a t as t h e oil gained in weight t h e density increased, while t h e volume increased t o a maximum and then slowly decreased. Except for t h e determinations of Sabin, of Thompson, and of Friend, there are no d a t a known t o t h e writer 1
3 4
6
J . Soc Chem. Ind., 10 ( 1 8 9 1 ) , 19. J. A m . Chem. Soc., 25 ( 1 9 0 3 ) , 7 1 1 ; 27 (1905), 605. THIS JOURNAL, 3 (1911), 8 4 . J . Chem. S o d , 111 (1917), 162. T r a n s . A m Inst. of Chem. Eng., 8 (1915), 251.
6 LOC
CiL.
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
638
FIG. 3-CHANGES
IN
CONSTANTS W I T H GAININ WEIGHT
showing the variation of t h e constants with gain in weight of raw linseed oil on exposure t o atmospheric oxidation. I n 1911 t h e writer exposed two samples of raw linseed oil in shallow glass dishes of approximately 12.5 cm. diameter in a dust-proof glass top cabinet which permitted circulation of air. I n order t o prevent the formation of a skin, tl.2 oils were thoroughly stirred a t least twice a day. At intervals the oil in each dish was thoroughly mixed and t h e specific gravity and iodine number determined, with the results as shown in Table I and Fig. I . TABLEI-EFFECT OF EXPOSURE ON R A N LINSEEDOIL
Age Days 0 7 14 21 28 35 42 63 84 105
NORTHAMERICAN Sp. Gr. lSSo Iodine No. 15.5O C. (Hanus)
LA PLATA Sp. Gr. ' c. Iodine N o . l m (Hanus) 173.0 172.4 171.9 171.8 171.5 170.0 168.6 166.4 160.6 154.9
By withdrawing portions of the oils for determination of t h e constants, t h e v\,lumes of t h e oils were gradually reduced, t h u s increasing the oil surface per gram of oil; or, in other words, decreasing t h e thickness of t h e oil layer. Now, since i t is well known t h a t , other things being equal, thin layers d r y more rapidly t h a n thick layers, these experiments suggested t w o questions : First, given layers of different thicknesses, a r e t h e changes in the constants the same for the same change in weight? Second, what is the quantitative effect of thickness of layer upon the rate of change in t h e constants? I n or'der t o determine t h e variation of t h e constants for determined gainsin weight, some pure, raw North American linseed oil was exposed in I O shallow round glass dishes, eight of 9.2 cm. diameter and two of 9.7 cm. diameter, a n d t h e dishes kept in a glass top cabinet protected from dust but permitting circulation of air.
OF
Vol.
11,
No. 7
R A N LINSEED OIL
About 7 0 g. of oil, accurately weighed, were placed in the eight smaller dishes, and about 36.9 g. in t h e two larger dishes. Each dish held throughout t h e test a glass stirring rod. Twice daily each sample was thoroughly stirred and a t intervals t h e gain in weight noted. A t longer intervals, the samples, one by one, were removed from t h e cabinet and certain constants determined. The length of exposure was limited by t h e formation of a skin, which would destroy t h e homogeneous character of the sample. TABLE11-PER
CENT
GAIN IN WEIGHTOF RAN LINSEEDOIL
0.95 Sq. Cm. 2.0 Sq. Cm. Oil Surface Oil Surface Age Per Per Days Gtam Oil Gram Oil 1 -0.05 -0.04 -0.05 -0.015 2 .... 3 -0.035 -0.025 +O.Ol 5 +O.Ol 7 .... .... 8 0.05 0.03 .... 9 0.04 0.065 11 .... 0.04 12 0.10 .... 14 .... 16 0.06 0.115 .... 18 .... 19 0.07 0.135 .... 20 22 0.08 .... 0.18 .... 23 .... 24 0.11 0.20 ... 26 0.15 .... 28 0.24 .... 29 0.19 0.32 31 0.36 34 0.23 0.42 37 0.25 0.47 .... 39 .... 0.28 40 .... 0.50 41 43 0.33 .... .... 0.61 44 .... 45 0.34 .... 0.70 46 0.77 47 0.35 0.86 49 0.39 .... 51 0.99 .... 0.45 52 .... 1.16 53 1.37 0.48 55 1.74 58 0.525 2.00 .... 60 61 .... 0.60 .... 2.25 62 .... 63 0.625 .... 2.76 65 .... 66 0.655 3.25 67 .... 68 0.69 .... 69 3.71 70 4.02 0.71
....
Axe D a
