ANALYTICAL EDITION
226
that if we use 100 times less hydrogen peroxide, which is still considerably in excess of the theoretical amount, we get a complete oxidation and we need no longer be very particular as to the purity of the reagent. One should certainly not infer from our paper that Francis and Parsons did not use a blank. We intended only to say that for our conditions we should need a blank, and that we prefer to use directions which make such a blank unnecessary for us. (2) We agree with the letter of Francis and Parsons that the “prudent chemist will desire to have this information’’-that is, the knowledge of the magnitude of the errors which are compensated by our method of making a new standard for every analysis. Although we do not mention it in our paper, we have made many blanks before we were able to obtain consistently good results. As to the statement of Francis and Parsons that we used nearly six times more sulfuric acid than they did, there was indeed an error on our part. It was produced by the following cireumstances: At the start of our work we tried t o duplicate as well as possible the work of Francis and Parsons. On page 266, they write that they use for each experiment 7 ml. of a mixture containing 1 ml. of 2 N sulfuric acid in 100 ml. of solution. From this we calculated that they used 0.14 ml. of 1 N sulfuric acid in each experiment, On page 267, they write that in each experiment the solution was made just alkaline by the addition of 0.5 to 1.0 ml. of 1 N potassium hydroxide. Since we did not understand the reason for this difference, we took such an amount of sulfuric acid as would be neutralized by 0.8 ml. of 1 N potassium hydroxide. We were in this way following a t least the spirit of the publication of Francis and Parsons. When writing our paper, we unfortunately failed to quote the original text of Francis and Parsons. We quoted the directions which we were using, having forgotten that we had made this alteration. We are sorry for this mistake. From the letter of Francis and Parsons, it is evident that there was no mistake in their publication. It may be interesting, therefore, to find out why they needed 0.5 to 1.0 ml. of 1 N potassium hydroxide in order to neutralize a solution to which they had added only 0.14 ml. of 1 N sulfuric acid. The explanation lies, we believe, in the fact that Francis and Parsons used their method for the analysis of combustion gases which contain carbon dioxide and sulfur dioxide. Assuming 20 per cent carbon dioxide in the fume gases (which is the theoretical maximum) and assuming 5.5 per cent sulfur in the coal, we find that 7 ml. of the aqueous oxidizing solution will absorb carbon dioxide equivalent to 0.07 ml. of 1 N potassium hydroxide, whereas the sulfuric acid produced by oxidation of 1 liter fume gas will need 0.38 ml. of 1 Nalkali. Furthermore, we need about 0.03 to 0.05 ml. of normal alkali in order to get a good alkaline reaction toward litmus paper. This makes altogether: 0.14 ml. 0.07 ml. 0.38 ml. 0.05 ml. b.ae ml.
1 N KOH for neutralization of added HaSOa 1N 1N 1N 1N
KOH for neutraljzation of COz KOH for neutralization of HBOt from sulfur KOH excess KOH
This amount of potassium hydroxide is well within the limits stated by Francis and Parsons. This shows that in our case we were justified in adding considerably more sulfuric acid than Francis and Parsons used in order to make the oxidation in a solution of about the same acidity. We did not, however, realize a t the time why we had to add more sulfuric acid, and we failed to indicate in our paper that the directions, which we said were the ones of Francis and Parsons, had been modified by us. (3) It is perfectly right to say that we confirmed the accuracy of the method of Francis and Parsons within the limits claimed by these authors-that is, 5 per cent. We may even say more than this. Our work has shown that the acid absorption and oxidation of nitrogen peroxide as dis-
Vol. 3, No. 2
covered by Francis and Parsons enable us to reach an unusually high accuracy. As described in our paper, we found in sodium nitrite (present 0.02 mg. of nitrogen) in seven consecutive experiments, 101, 101, 103, 101, 101, 98, and 101 per cent of the theory, and in eight consecutive nitrogen oxide determinations (present about 0.045 mg. of nitrogen), we found 101, 101, 100, 98, 100, 102, 102, and 98 per cent of the theory. In dynamite fumes especially low in nitrogen peroxide, we found successively 95.1, 102.3, 102.3, 95.1, and 105.2 per cent of the average, and in dynamite fumes of ordinary composition, we found 99, 102, 98, 102, and 99 per cent of the average. For these 25 determinations our average error is 1.9 per cent. J. PICCARD ERNESTG. PETERSON C. D. BITTING HERCULES POWDERCOMPANY KENVIL,N. J. January 12, 1931
A Study of the Official Method of Bleaching Test of the American Oil Chernists’ Society Editor of Industrial and Engineering Chemistry: We are sorry that Ma and Withrow f I N D . ENG.CHEM.,Anal. Ed., 2,374 (1930)] used the expression
l o ~ o ~ - - ~as’ a measure:
of the degree of bleach. According to Lambert’s and Beer’s laws, the concentration of coloring matter in a liquid is proportional to the negative logarithm of the amount of light transmitted by the liquid. Tables of color units based on the amount of light transmitted by a liquid are given by Meade and Harris [J. IND. ENG.CHEM., 12, 687 (1920)] and by Peters and Phelps [Bur. Standards, Tech. Paper 338 (1927) 1. Using such systems of units, Teeple and Mahler [IND. ENG. CHEM., 16, 498 (1924)l have shown that the action of adsorbents on oils follows Freundlich’s equation for a while and then the line breaks. I n our work we have never found such a break in the case of aqueous solutions, but have invariably found it in the case of vegetable oils, whether using fuller’s earth, activated carbon, or mixtures of these bleaching agents. Using the data for the green in Table I11 of the article by Ma and Withrow, and the color units for green which appear in Chem. Met. Eng., 28,541 (1921), Table I, we find that the points representing 1 to 4 per cent, inclusive, of fuller’s earth follow Freundlich’s equation and ,that the break in the isotherm appears between the points representing 4 and 5 per cent earth. The use of the Meade-Harris color units for the concentration terms in Freundlich’s equation enables one to predict the action of fuller’s earth or carbon on a vegetable oil from a few experimentally determined points. We hope that investigators of the action of adsorbents on oils will use this method of reporting their results. The use of color units proportional to the logarithm of the transmission has the advantage that such units can be converted to Lovibond red units by a factor. M. T.SANDERS ATLASPOWDERCOMPANY DEL. WILMINGTON, November 14, 1930
Correction-In the article “Determination of Chromium and Vanadium in Ores and Alloys after Oxidation with Perchloric Acid,” by Hobert H. Willard and R. C. Gibson, ING. ENG.CHEM., Anal. Ed., 3, 88 (1931), the number 50.66, on page 89, line 15, of the first column, should read 51.66.
