July,
1920
T H E JOURNAL OF I N D U S T R I A L A N D ENGINEERING CHEMISTRY
one-tenth aliquot parts taken. These are heated t o 70’ C., about 15 cc. of I : 4 sulfuric acid added, followed b y a decided excess of sodium acid sulfite solution, a n d t h e thiocyanate precipitated with a hot I O per cent solution of copper sulfate. After standing I O min. t h e C u C N S is filtered off through a Gooch crucible, t h e bottom of which is covered with a circle of filter paper, followed b y a layer of paper pulp which is in t u r n partly covered b y a small piece of filter paper. Too long standing previous t o filtering is t o be avoided as it increases t h e tendency of t h e C u C N S t o pass through t h e filter as a colloid. T h e impure C u C N S is washed with hot water of about t h e same temperat u r e as t h e original solution which was filtered. Since a little C u C N S sometimes passes through t h e filter i n t h e colloidal form, t h e filtrate, if clear, should be removed and discarded as soon a s t h e last of t h e liquid h a s been poured through t h e filter. If a l i t t l e of t h e precipitate now passes through t h e filter upon washing, a quantity of paper pulp may be added t o i t and t h e wash water refiltered through a n ordinary paper filter, washed with hot water, and combined with t h e major portion of the C u C N S precipitate. T h e residue, consisting chiefly of paper pulp a n d C u C K S , is treated with 2 5 cc. of N sodium hydroxide, a little bromine water is added t o oxidize the copper, a n d after a few minutes t h e paper pulp is filtered off a n d thoroughly washed with hot water. A little more bromine water is added t o t h e alkaline solution and i t is digested a t t h e boiling point for one hour. It is made slightly acid with hydrochloric acid, t h e bromine boiled off, and t h e solution taken t o dryness. T h e dry residue is taken u p with hot water containing a little HC1 a n d filtered from silica. T h e sulfur present originally in t h e CiICNS is t h e only sulfur now left i n the solution and i t is entirely i n t h e form of sulfate. This may now be precipitated with barium chloride a n d determined i n t h e usual manner and t h e thiocyanate calculated. For t h e purpose of checking t h e metho‘d, t h e thiocyanate content of t h e liquor was determined b y t h e above method and also t h e thiocyanate content of t h e liquor t o which a known a m o u n t of potassium thiocyanate had been added. T h e results indicated t h a t thiocyanate i n ammoniacal liquor can be determined b y this method t o within 0.01 g. per liter. Aside from t h e exercise of a little technique in filtering, t h e analysis proceeds quite nicely. VOLUMETRIC METHOD FOR THE DETERMINATION O F DIASTATIC CAPACITY By J. T. Flohil CERRAI.PRODUCTS COMPANY, MANITOWOC, WISCONSIN Received January 16, 1920
AYs per cent malt solution is prepared according t o Lintner.’ One cc. of t h e extract is introduced into IOO cc. of a 2 per cent soluble starch solution i n a zoo cc. flask, left t o a c t for exactly one hour a t 20’ C., then treated with IO cc. of 0.1 N sodium hydroxide t o s t o p t t h e diastatic action, and diluted with water t o t h e 200 cc. mark. 1
Z . prakl. Chem., 1886, 386.
677
Twenty-five cc. of this solution are transferred t o a I O cc. each of Fehling’s Solutions I and I1 added, a n d t h e volume brought u p t o 50 cc. with 5 cc. water. T h e mixture is boiled slowly for z min., and immediately cooled under t h e cold water faucet, b u t not much under 25’. T e n cc. of a 30 per cent potassium iodide solution, or 3 g. potassium iodide and I O cc. of a 2 5 per cent sulfuric acid solution, are added successively and t h e liberated iodine titrated with a 0.1 N thiosulfate solution t o a creamy yellow color, t h e soluble starch present serving as a n indicator. 300 cc. Erlenmeyer flask, exactly
CALCULATION
Let p cc. be t h e amount of thiosulfate used in this titration, ‘IZ cc. t h e amount of thiosulfate used i n a blank test ( 2 5 cc., 5 cc. water, 2 0 cc. Fehling’s solution); t h e n n - p = m is t h e amount of thiosulfate equivalent t o t h e copper sulfate reduced by t h e maltose sugar. According t o Lintner, if I cc. of a j per cent malt infusion in 100 cc. of 2 per cent starch solution produces just enough maltose t o reduce 50 cc. of Fehling’s solution its strength is 100’. This solution diluted t o zoo cc. of I per cent starch solution will also reduce 50 cc. of Fehling’s solution, and 2 5 cc. will reduce 6 . 2 5 cc. of Fehling’s solution. We here assume t h a t t h e quantity of copper sulEate reduced is proportional t o t h e amount of maltose present, without making a n appreciable error. If 20 cc. of the Fehling’s solution is equivalent t o n cc. 0.1 N thiosulfate, then I cc. is equivalent t o n / 2 0 cc. thiosulfate. If 2 5 cc. of t h e solution mentioned in the beginning of this article reduce Fehling’s solution equivalent t o 6.2 j n / 2 0 cc. of thiosulfate, t h e Lintner value is 100’. If 2 5 cc. of t h e solution reduce Fehling’s solution equivalent t o m cc. of thiosulfate, its strength is m m X I O O = 3 2 0 -- degrees Lintner. 6.25 n n 20
ExA&wLE--In a blank test t h e a m o u n t of iodine set free b y t h e copper sulfate was equivalent t o 2 7 . 0 cc. 0.1N thiosulfate, or ti = 27.0. I n t h e actual test t h e amount of iodine set free by t h e copper sulfate was equivalent t o 15.0 cc. 0.1N thiosulfate; therefore m = 2 7 . 0 1 5 . 0 = 1 2 . 0 and t h e diastatic capacity is 3 2 0 1 2 / 2 7 or 1 4 2 ’ Lintner. THE UNIFORM COMF OSITTON OF COMMERCIAL “STEARIC” AC. DS, AND ITS EXPLANATLON By Ben H. Nicolet MELLONI N S T I T U T E
O F INDUSTRIAL RESEARCH, PITTSBURGH, Received October 27, 1919
PA.
Sometime ago t h e writer had occasion t o make some comparative tests on a number of samples of commercial stearic acids chosen a t random. T h e titers were surprisingly uniform throughout t h e series and when these were corrected for t h e small and varying iodine numbers which t h e different samples showed, t h e agreement ‘became startling. T h e maximum variation in t h e corrected titers for t h e six samples, coming from five entirely different sources, was less t h a n 0 . 5 ~ .
