T H E J O U R N A L OR 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
1126
t h a t i t was not t h e sugar of t h e syrup, b u t did not give a n y definite evidence as t o what t h e compounds causing the increased activity of t h e yeast might be. IV.-Partially dried grapes may be used instead of syrup during fermentation t o increase t h e sugar content and invigorate t h e yeast. Therefore, no expensive evaporating system is necessary in t h e application of t h e new method. ‘IT-Where the wine made by t h e new method was not filtered and carefully handled, it was spoiled b y t h e growth of “tourne” bacteria. Where i t was racked clear or filtered after fermentation and kept in wellfilled packages, it kept well and developed a n agreeable “rancio” or “sherry” flavor. Whether t h e method will become important commercially remains to be seen. It was applied on a large scale during t h e past season b y several large companies in California, b u t t h e results of this work are not available for publication. VITXCULTURE DIVISIOI UNIVERSITY OF CALIFORNIA, BERKELEY
TOTAL CARBON IN SOIL BY WET COMBUSTION By C. J. SCHOLLENBERGER Received August 23, 1916
The determination of total carbon in soil is necessary in certain soil investigations. Of t h e several methods used, t h a t of combustion in a furnace! absorption and weighing of the carbon dioxide obtained is probably the most accurate, provided t h e necessary precautions are observed. T h e latter include not only t h e complicated purifying and drying train common t o all gravimetric carbon determinations, b u t a second combustion tube n-ith copper oxide or some similar arrangement t o insure complete oxidation of volatile carbon compounds which may be distilled off before a temperature sufficiently high €or complete combustion has been attained. -4 further precaution necessary in t h e case of soils high in carbonate carbon is a determination of carbonate in the residue after the ignition. In this connection it may be well t o cail attention t o the fact t h a t the wet combustion-volumetric method described b y Ames and Gaitherl is capable, with slight changes, of affording results which compare very favorably with those obtained from a furnace combustion and gravimetric determination. The changes referred t o consist in t h e use of a mixture of phosphoric and sulfuric acids, instead of sulfuric acid alone, with chromic anhydride as t h e oxidizing agent, in t h e substitution of barium hydroxide for sodium hydroxide as t h e alkaline absorbent for carbon dioxide, and in the replacement of the .modified Camp absorption t u b e described in the original article b y Meyer’s absorption apparatus or Truog’s bead together with changes in procedure made necessary by t h e changes in reagents employed. T h e apparatus used and t h e method of operation are practically the same as those described in t h e article first cited, with the changes as noted; t h e absorption apparatus being filled with t h e alkaline absorbent, a gentle suction is turned on t o facilitate the 8
THISJOURIAL,
* dbid., 7
6 (1914), 561.
(1915), 1045.
Vol. 8 , NO. 1 2
addition of t h e reagents. T o t h e sample ( I t o 3 g.) in t h e boiling flask is added I O cc. of the oxidizing mixture made as follows: chromic anhydride 8 j g. dissolved in 1 0 0 cc. water and diluted t o 2 5 0 cc. with 8 j per cent phosphoric acid. The I O cc. portion of oxidizing mixture is followed b y z j cc. 85 per cent phosphoric acid and b y Z j cc. concentrated sulfuric acid. T h e mixture is heated rapidly a t first, b u t with a lower flame when t h e reaction is well started; after t h e chromic acid is largely decomposed, a more intense heat may be used, b u t very hard boiling is unnecessary; the heating should be continued about 3 0 min. after boiling begins. A current of purified air is aspirated through the apparatus in volume just sufficient t o prevent t h e hot acid mixture being forced up t h e stem of t h e separatory funnel for addition of reagents. T h e apparatus should be so arranged t h a t the condensed water will run down the outside of the stem of this funnel and not drop directly into the hot acid; this simple precaution will prevent much trouble and breakage of apparatus. The partial substitution of phosphoric for sulfuric acid reduces t o a negligible quantity the fuming noticed when sulfuric acid alone is used; heavy fumes of sulfuric acid are objectionable, not only for t h e reason t h a t they cause a consumption of the alkaline absorbent, b u t because they prevent complete absorption of carbon dioxide. Phosphoric acid alone was tried, but invariably gave results too low; a certain amount of sulfuric acid is absolutely necessary t o insure complete oxidation. The determination is completed b y titrating the barium carbonate as described by Cain1 or b y titrating the excess of barium hydroxide as described b y Truog.2 The latter method, while not absolutely accurate under all conditions, as was pointed out in a former article3 is sufficiently so for most purposes a n d is very much more rapid and convenient; with either method, t h e solutions used should be standardized against a sample of known carbon content. Blanks should be r u n for carbon in reagents, etc. PER CENT TOTAL CARBON I N SOIL BY SEVERAL hcETHODS Sample 1 2 3 4 Furnace combustion, Gravimetric., . . , 0 . 9 4 2 . 6 9 1 . 1 3 0.88 Wew wet combustion, Volumetric, B a ( 0 H ) z . . . . . . . . . . . . . . . . . . . ~. . . 0.94 2 . 6 6 1 . 1 3 0.87 Old wet combustion, Volumetric, NaOH. . . . , . . . . . . . . . . . . . . . . 0 . 9 0 2 . 6 2 1.10 0.80 Parr method.. . . , . . . . . . . . . . 0 . 8 3 2 . 6 6 1.10 0.97
.. . . .. . . . .. . . .
..
.
5 2.95
2.84 2.72
,.
I n t h e table are presented results obtained on five samples of soil by the gravimetric method (com6ustion with copper oxide in combustion tube, absorption and weighing of carbon dioxide). by the wet combustion-volumetric method as modified, titrating excess barium hydroxide without removal of carbonate, b y t h e met combustion-x-olumetric method as originally described, and b y the Parr method of combustion in bomb with sodium peroxide and measurement of carbon dioxide in gas burette. The results tabulated are from the averages of a t least two closely agreeing determinations. OHIO
1
AGRICVLTVRAL EXPERIMENT STA’IIOY WOOSTER, OHIO
THISJOURNAL, 6 (19141, 465.
* Ibid., 3
7 (1915), 1045. I b i d . , 8 (1916), 427.
