ANALYTICAL EDITION
AUGUST 13. 1938
43 1
A wooden top was then fitted over the Celotex and around
to show which heaters are in operation. Above the instrument panel and adjacent to the main supply line switches are the automatic cutoff switches Khich connect with bulb G in the constant-temperature tank.
the lids of the pressure vessel covers. Covers of wood a n d Celotex were made to place over the pressure vessels and temperature readings inside the 5.75 X 7 inch stainless-steel vessels were as follows :
Temperature inside Pressure Vessels
Position inside Pressure Vessel
Tempei ature
T a t e r Temperature
The original plans for the equipment specified that the pressure vessels be bolted to the metal tables, using a gasket to insulate the pressure vessel from the table. After the installation was made according to these plans the following temperatures were obtained inside the 5 X 11 inch pressure vessel:
1 inch from top 1 inch from bottom
69 5 69 5
70 70
Position inside Pressure Vessel Inches from t o p 1 3 4 6 7 10
FIGURE9. SAFETY RELEASE
Temperature
K a t e r Temperature
68.5
70 70 70 70 70
c.
68.5
69.0 69.5 (0.0 70.0
c.
c.
c.
K i t h these data a\-ailable it is possible to adjust the temperature of the circulating water to maintain 70" C. (158' F.) inside the pressure vessels. Aging studies making use of the flexible facilities of this improved oxygen pressure-aging apparatus vi11 be presented later.
Aclinowrledgment Acknowledgment is made to N. E. Raber of the B. F. Goodrich Engineering Department, who designed the automatic cutoff valve (Figure 8). Literature Cited
70
Similar readings inside the 5.75 X 7 inch stainless-steel vessels were low and more variable. In order to correct this variation within the pressure vessel, the tables were covered with Celotex and the pressure ressels then mounted in place.
(1) Bierer and D a v i s , ISD.ESG. CHEM.,16, i l l - 1 7 (1924). ( 2 ) Ingmanson and Kemp, Ibid., 28, 889-92 fl936). RECEIVED April 2, 1938. Presented before the Division of Rubber Chemistry, American Chemical Society, a t its meeting in Desroit, hlich., )larch 28 and 29. 1938.
Determination of Formaldehyde in Dilute Solutions and in the Presence of Interfering Substances OSCAR HEIRI, East Hempstead, K. T.
FLUID pharmaceutical preparation, which a t the time of analysis contained about 0.003 per cent of formaldehyde, could not be even roughly analyzed for its formaldehyde content by the ammonia (@, cyanide ( 1 , 6 ) , hydrogen peroxide (S), and iodine (6) methods. This was due in part to the flavoring agent, one ingredient of which was oil of cinnamon (aldehyde). The deep red color of the preparation prevented the use of procedures depending upon production of colors. On attempting to isolate the formaldehyde by distillation, it was found that the small amount of formaldehyde present was reduced to pract'ically zero. Satisfactory results were obtained with a modification of the silver method (4) used with niixt'ures of known formaldehyde content. This modification has also the advantage that reducing sugars do not interfere.
Procedure Exhaust the aqueous or aqueous alcoholic fluid with etherpetrolic ether (1 2) to remove flavor, etc. Four to five extractions, each with one-half volume of solvent, are usually sufficient. To 10-cc. aliquot, add in rapid succession 100 cc. of 0.1 'If silver nitrate, 1 cc. of hydrochloric acid (37 per cent), and 3 cc. of sodium hydroxide ( 2 5 per cent). Whirl once after each addition. Finally whirl 10 minutes for good contact. Filter through paper and wash until chloride free. Pour warm nitric acid (1 3) onto precipitate to dissolve all reduced silver. Wash with hot water and titrate with 0.1 hr ammonium thiocyanate and ferric alum.
+
+
2 Ag
=
ICHgO.
d determination can be done in about 30 minutes. The average percentage reproducibility observed is of the order of two units in the third decimal place.
A mixture was made of 10 cc. of the sample under investigation plus 10 cc. of an aqueous 0.20 per cent formaldehyde, n e d g made u p from about 37 per cent stock and for the purpose of introducing all like interfering factors, also shaken out mith the ether-petrolic ether. This mixture analyzed 0.097 per cent; the actual content was calculated as 0.101 per cent (the average of 0.003 and 0.20 per cent). The aqueous 0.20 per cent formaldehyde made from about 37 per cent stock analyzed 0.19 per cent forinaldehyde. After extracting with ether-petrolic ether, i t still showed 0.19 per cent, while the Association of Official Agricultural Chemists cyanide method gave 0.009 per cent in both cases. An approximately 0.2 per cent solution of acetaldehyde, a little freshly made silver chloride, and a slight excess of sodium hydroxide turn the silver chloride a light bluish gray after about one minute, whereas 0.2 per cent formaldehyde, under the same conditions, turns the silver chloride black immediately. Literature Cited (1) Assoc. Official Agr. Chem., Official and Tenta.tive Methods, 4th ed., p. 62 (1935). ( 2 ) Craig, A. G., J . Am. Chern. Soc., 23, 642 (1901). (3) Haywood a n d Smith, Ibid., 27, 1188 (1905). (4) Heim, IND.ESG. CHEM., Anal. Ed., 1, 128 (1929).
( 5 ) McDonnell, C. C., U. S. Dept. Agr. Bur. Chem., Bull. 132, 47, 48 (1909). (6) Romijn, 2. anal. Chern., 36: 18 (1897) RECEIVED March 28, 1938.
