= =94
T H E J O U R N A L O F I N D U S T R I A L A N D EhTGINEERING C H E M I S T R Y
within about I O per cent t h e amount of soy-bean oil which has been mixed with linseed in a paint, provided only these two oils are present in t h e saponifiable portion of t h e vehicle. SUMMARY
( I ) -4 method has been developed for t h e detection of substitutes in linseed oil and paints, based upon t h e determination of t h e amount of ether-insoluble hexabromides obtained b y brominating t h e f a t t y acids under fixed conditions. (2) This method is less complicated t h a n some of those previously proposed, and gives more concordant results t h a n t h e older methods. (3) T h e hexabromide value of pure extracted or expressed linseed oils varies between comparatively narrow limits, a n d is, on t h e average, about 4 2 . (4) T h e average hexabromide value of pure soy-bean oil is 6, of t u n g and fish oils 0.0. The latter, however, gives ether-insoluble octobromides which can be readily separated from t h e hexabromides of t h e vegetable oils because of their insolubility in warm chloroform. (5) T h e proportion of linseed oil in a mixture of this oil with soy-bean, tung, or fish oils, can be determined much more closely b y means of t h e hexabromide t h a n b y t h e iodine value of t h a t mixture. (6) It appears probable t h a t b y t h e method developed a close approximation of t h e composition of t h e non-volatile vehicle of a paint may be obtained, b u t further study of t h e applicability of this hexabromide method t o paint analysis is desirable. * NAPHTHALENE SULFONIC ACIDS. 111-AN ALTERNATIVE METHOD FOR THE QUALITATIVE DETECTION O F NAPHTHALENE-2,7- AND 1,6-DISULFONIC ACIDS' By Joseph A. Ambler COLORLABORATORY, BUREAUO F CHEMISTRY,WASHIKGTON, D. C . Received August 18, 1920
I n t h e second paper of this series b y Ambler a n d Wherry2 t h e qualitative detection of t h e 2,7- and 1,6disulfonic acids is made b y means of a microscopic examination of their @-naphthylamine salts after t h e other common naphthalene-sulfonic acids have been removed. While this microscopic examination is t o be preferred, another method of detecting these t w o acids may be used as a confirmatory test, or in case a microscopic examination cannot be made conveniently. The analysis is carried out exactly as in t h e former method up t o t h e point where t h e mixed P-naphthylamine salts of t h e 2,7- and 1!6-acids are submitted t o microscopic examination. T h a t is, all t h e naphthalene-P-, 1,5-; 2,6-, and a-sulfonic acids have been removed. T h e salts from t h e qcetone extraction are dried a t I O O O and then treated by t h e following method: TEST F O R NAPHTHALEXE-2,7-DISCLFONIC
ACID
A portion of t h e acetone-insoluble dry salts is boiled 1
Presented before the Division of Dye Chemistry a t the 60th Meeting
of the ilmerican Chemical Society, Chicago, Ill., Septemher 6 to 10, 1920. 2
THIS J O U R N A L , 12 (1920), 1085.
Vol.
12,
NO. I Z
with 4 or j cc. of a mixture of four volumes of 95 per cent alcohol and one volume of water. Complete solution should t a k e place, b u t if this does not occur, t h e insoluble material' is removed b y filtering. On cooling t h e alcoholic solution, t h e /?-naphthylamine salt of t h e 2,7-disulfonic acid crystallizes out. T E S T F O R NAPHTHALENE-I,6-DISULFONIC ACID
T h e remaining dry salts are covered with water, heated t o boiling, and t h e /?-naphthylamine removed b y titrating with normal sodium hydroxide solution, using phenolphthalein as indicator. T h e volume of alkali used is noted. T h e amine is filtered off after cooling t h e solution, and t h e filtrate evaporated t o dryness: T h e dry sodium salts are taken up in t w i c e as much water as t h e normal alkali used i n freeing t h e amine. T o a measured volume of this solution, a n exactly equal volume of concentrated sulfuric acid (sp. gr. 1.84) is added. T h e solution is cooled a n d crystal formation induced b y rubbing with a stirring rod. T h e solution is allowed t o s t a n d for several hours with frequent rubbing a n d agitation before a negative result is assured. Under these conditions, t h e 1,6-disulfonic acid gives a crystalline precipitate of t h e sodium salt, which sometimes forms slowly, while t h e 2,7-acid remains i n solution. DISC US SI 0N
I n t h e test for t h e 2,7-disulfonic acid, t h e P-naphthylamine salts of all t h e preceding. acids will crystallize from t h e dilute alcohol. Hence t h e necessity of t h e complete removal of those acids. Further, t h e salt of t h e 1,6-disulfonic acid may crystallize out, if too large a quantity of t h e dry salts is used. A little practice with t h e pure salts, however, will give t h e analyst t h e necessary skill in manipulation and interpretation of results. T h e test for t h e 1,6-disulfonic acid is delicate t o about 16 parts per. thousand. T h e directions make approximately an 8 per cent solution of t h e mixed salts. Hence, mixtures of t h e two acids which contain more t h a n one part of t h e 1,6-acid t o five parts of 2,7-acid, may be tested safely b y this method; and if t h e 2,7-isomer is partially removed with diluted alcohol, mixtures containing even a smaller proportion of t h e 1,6-acid may be tested. The 2,7-isomer does not precipitate unless t h e solution contains about I O per cent of t h e 2,7-salt. Since t h e directions for t h e test for t h e 1,6acid are such t h a t an approximately 8 per cent solution of t h e sodium salts is obtained, there is no danger of t h e 2,7-acid being precipitated instead of t h e 1,6-acid. These relations are shown more clearly in t h e accompanying table. These results were obtained b y . of solutions of t h e two salts of t h e taking 5 - c ~ samples concentrations noted, and adding one cc. of concentrated sulf6ric acid, sp. gr: 1.84, allowing t h e mixture t o cool, and giving i t plenty of time t o crystallize. A second cc. of sulfuric acid tvas then added, and t h e experiment repeated. This process was repeated until 5 cc. of acid had been added. The table shows t h e result after t h e addition of t h e fifth cc. of acid. 1 8-Naphthylamine naphthalene-2,6-disulfonate, which crystallizes from the boiling solution upon cooling and is only slightly soluble in this reazent.
