I N D U S T R I A L A N D ENGINEERING CHEMISTRY
May, 1928
first suggested this as a means of improving the end point. The excess method has not proved satisfactory for the oand p-cresols. The results were too much affected by the analytical conditions. Pence," who studied the quantitative bromination for resorcinol, allowed the bromination mixture to stand for 5 minutes after the addition of the iodide. His method has been used, with litble modification, in this investigation and good results were obtained. T a b l e I-Results
b y Excess M e t h o d PERIOD BRO- SAM-
OF MINE PLES M E A N DILU- BROMI-EQUIV-ANA- RESAMPLE SOLVENT TION NATION ALENT LYZED SULT Grams Cc. H20 M i n . % 0.5-0.6 h-aOH Phenol 50 5-30 3 Brz 5 99.89 0.5-0.7 NaOH 100 0-Chlorophenol 30 2 Br2 4 99.87 o-Nitrophenol 0.5-0.7 NaOH 50 30 2 Brz 4 99.77 m-Nitrophenol 0.5-0.6 NaOH 50 5-30 3 Brz 4 99.88 $-Nitrophenol 0.7-0.9 NaOH 50 5-30 2 Brz 4 99.90 2,4-Dinitropnenol 1.5-1.8 h-aOH 50 30 1 Br? 4 99.92 Salicylic acid 0.5-0.6 NaOH 50 5 99.86 30 3 BIZ m-Hydroxy benzoic acid 0.5-0.6 NaOH 15 3 Brz 4 50 99.85 Methylsalicylate NaOH 0.6 60 99.82 7 30 3 Brz Phenylsalicylate 0.4-0.5 NaOH 50 99.87 5 30 6 Brz Acetylsalicylic acid 0.6-0.7 h-aOH 50 30 3 Brz 7 99.84 m-Cresol 0.5-0.6 NaOH 1 3 BIZ 50 99.75 6 Resorcinol 0.5-0.6 Hz0 1 3 BIZ 4 100 99.95 @-Naphthol 1.2-1.5 NaOH None 15-20 1 Brz 99.89 5 Thymol 0.4-0.8 h-aOH None 15-20 2 Br? 99.77 7 Aniline 50 99.92 0.5-0.6 HC1 5-10 3 Br2 5 P-Chloroaniline 1 -1.2 HCI 99.93 4 50 10 2 Br? o-Nitroaniline 0.5-0.6 HCI 30 2 Brz 100 99.86 4 m-Nitroaniline 0.5-0.6 HCI 30 3 BIZ 50 99.89 5 Acetanilide 99.84 0.5-0.7 HCI 5-10 3 Brz 50 5 Sulfanilic 30 3 Brz 5 50 0.5-0.6 NaOH 99.98 Metanilic acid 0.5-0.6 NaOH 99.80 5-15 3 BIZ 5 50 Anthranilic 0.5-0.6 NaOH 99,89 30 3 BIZ 5 50 m-Aminobenzoic 10-15 3 Brz NaOH 0.5-0.6 50 4 99.86 m-Toluidine 5-10 3 BIZ 0.5-0.6 HCI 50 99.87 6
SUBSTANCE
The excess method, in the absence of a special so!vent, was found not be applicable to p-naphthol and thymol. Chloroform was adopted as the best solvent for these two, being not only a suitable solvent but a t the same time fairly stable toward bromine. Five cubic centimeters were used for each analysis. Blank determinations were made under exactly the same conditions. Thus, even though the chloroform was slightly attacked by the bromine, an accurate correction was made. It was found best to cool the mixture slightly before acidifying because of the vapor pressure of the chloroform and to shake the flask gently, after acidifying, until the brominated precipitate dissolved in the solvent. I n the titration of the liberated iodine vigorous shaking was necessary just before the end point was reached, as the chloroform retains the last of the iodine rather tenaciously. 11
J. TND. ENO.CHEM.,3, 820 (1911).
547
Owing to their ease of oxidation, aniline and those compounds which yield aniline by hydrolysis (acetanilide) or which yield tribromoaniline on bromination through the replacement of a carboxyl or sulfonic acid group (sulfanilic acid, anthranilic acid, etc.) must be brominated a t a lower temperature, usually 10-15" C. I n certain cases, however. (0- and p-toluidines) good results could not be obtained, even when working a t much lower temperatures. For such types the excess method is of little value and the direct method is more applicable. The acetanilide was hydrolyzed before analysis by heating just to boiling for 10-15 minutes with 6 N hydrochloric acid. The solution was neutralized with sodium hydroxide, then made slightly acid with hydrochloric acid, and finally diluted to 250 cc. Low results were always obtained for p-nitroaniline. The brominated precipitate was very voluminous and it is probable that some incompletely brominated product was occluded. The excess method was not applicable to p-aminobenzoic acid. Instead of obtaining tribromoaniline, as would be expected (similar to the action of bromine on the ortho isomer), an insoluble dibromo derivative was formed, but a t the same time some tribromoaniline was also formed. The results were then high based on 2 Brz and low based on 3 Brz. Other compounds than those given in Table I have been tried (anisole, phenolphthalein, qvinol, dimethylaniline, benzidine, arsanilic acid, carbazole, etc.), but apparently good results cannot be obtained by the usual excess method. T a b l e 11-Results SUBSTANCE o-Cresol o-Toluidine $-Toluidine
by Direct T i t r a t i o n M e t h o d BROMINE SAMPLES MEAN SAMPLE SOLVENTEQUIVALENT ANALYZED RESULT Grams % 1 6-1.8 NaOH 2 Brz 3 100.04 1.5-1.8 HCl 2 Brz 3 100.08 1.5-1.8 HC1 2 BIZ 3 100.19
I n all cases where the excess method was not applicable the direct method was tried, but only in the cases given in Table I1 were fair results obtained. It would seem that this method as now carried out, seemingly simple though it may be, is not so accurate as the excess method. With the idea of improving the direct method, work has been started using an electrometric method as described by Fo-ilk and Bawden.'* N o t e A complete bibliography and a more detailed description of the work done is given in the original paper, including the melting and boiling points of the materials analyzed, suitably corrected, and compared with the best published values. 1%
J . A m . Chem. SOC.,48, 2045 (1926).
Transmissive Properties of New Glasses The number of inquiries which the Bureau of Standards received concerning the ultra-violet transmission of glasses and glass substitutes led them to issue Letter Circular 235 on this subject. This letter circular gives the results of ultra-violet transmission tests which have been made a t the Bureau of Standards upon a number of glasses transparent to the shortest wave lengths which the atmosphere permits the sun to furnish and common window glass. Using a filter method, direct measurements, with sunlight as source, of total transmission of various glasses for those ultraviolet solar rays to which common window glass is opaque were made during the noon hours of especially clear days from April to December, 1927. These measurements covered the solar spectral region to which common window glass is opaque (below about 310 mp). Table I gives for that region the total transmission found for several specimens. By means of spectral transmission curves an estimate of the relative transmissions of the various specimens for rays shut out by common window glass may be obtained by reading from
the curves, which are shown on a chart accompanying the letter, the values of the transmission a t 302 mp-the wave length of an intense mercury line of convenient value for making such tests. Transmission values for this wave length are also included in the circular. T a b l e I-Total T r a n s m i s s i o n s of Various Glasses w h e n New, f o r Ultra-Violet Solar R a y s t o W h i c h C o m m o n Window Glass Is O p a q u e TRADE NAME TRANSMISSION TRADENAME TRANSXISSION Per cent Per cent Fused quartz 92 Cel-o-glassb 20 Corex 92 Quartz-lite 5 Helioglass (Vioray)' 50 Flexoglassc 1 Vitaglass 50 Common window glass 0-5 a Vioray is the foreign trade name for Helioglass. b This consists of a fine wire screen whose interstices are covered with cellulose acetate. c This is a loosely woven fabric usually covered with paraffin.
A limited number of mimeographed copies of Letter Circular 235, with accompanying chart showing transmission of various window glasses when new, is available a t the Bureau of Standards.
