,
Acid-Base Adsorption. The baseadsorption capacity of charcoal is seen (Table V) to rise appreciably on treatment with oxygen at different temperatures to a maximum value at 400’ and to decrease thereafter. The acid adsorption capacity, which is very much lower in magnitude, follows the reverse order, being minimum at 400’. These facts have been reported (2, 3. 5, 6 ) , but no satisfactory explanation appears to have been offered. I t was thought of interest to correlate the capacity of charcoal to neutralize alkalies with the amount of carbon dioxide evolved from it on high temperature evacuation. The latter values expressed in milliequivalents per 100 grams are compared with the corresponding barium hydroxide values in Table VI in the case of the samples of charcoal described in Tables I and 11. I n most cases the amount of alkali neutralized by charcoal is almost exactly equivalent to the amount of carbon dioxide evolved from it on degassing at 1200’. This shows that the acid character as well as the base-adsorption capacity of charcoal is almost entirely due to the presence of the carbon dioxide complex contained in it. Charcoal activated in oxygen at 400’ contains the maximum amount of this complex and therefore it has maximum base-adsorption capacity. The amount of this complex decreases on treatment with oxygen a t higher temperatures and the base adsorption capacity decreases CorrespondingIy. The acid adsorption by charcoal increases when the carbon dioxide complex decreases, obviously because the charcoal surface is then less acidic. While the acid was adsorbed reversibly, as it could be removed almost completely by repeated washings with water, the alkali was adsorbed irreversibly, as very little of it could be removed in this manner. The charcoal samples treated with oxygen (3 liters per hour) at 400’ for 16 hours were subjected to evacuation a t temperatures varying from 100’ to 1200°, starting with a fresh sample a t each temperature. The amounts of gases evolved, together with the amounts of barium hydroxide neutralized by the residual samples, after evacuation a t the various temperatures. are recorded in Table IV. The evolution of water and carbon dioxide starts on evacuation in the 300’ to 400’ temperature range and is almost complete a t 750’. Carbon monoxide is evolved (in appreciable amounts) only from sugar charcoal; its evolution commences a t 750’ and appears to be complete at about 1200’. The capacity of charcoal to react with alkali decreases with increase in the temperature of evacuation and the decrease a t a particular temperature is almost equivalent to the amount of carbon dioxide eliminated from the
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charcoal a t that temperature (columns 4 and 5, Table IV). The agreement is striking in the case of sugar charcoal, which was almost free from ash. I n the case of the other two samples, the amount of the carbon dioxide given out a t a particular temperature (column 5) is somewhat larger than the corresponding decrease in the amount of alkali neutralized (column 4). This small difference appears to be due to some extra amount of carbon dioxide formed by oxidation of charcoal at high temperature by the small amount of silica and other metallic oxide ash contained in the samples. It may, therefore, be concluded that base-adsorption capacity of activated charcoal treated with oxygen is almost entirely owing to that part of the chemisorbed oxygen which decomposes on degassing a t high temperatures to give carbon dioxide. The view of some workers ( 7 7 ) , that all or almost all of the chemisorbed oxygen is involved in the sorption of bases from aqueous solution, is not substantiated. This also explains why IVelier and Young (70) could not properly correlate sorption of bases by charcoal with total oxygen. The observations recorded here indicate the importance of determining the disposition of the chemisorbed oxygen in evaluating charcoals and in understanding their behavior toward bases and acids. literature Cited (1) Arnell, J. C., McDermot, H. L., J . Phys. Chem. 5 8 , 492 (1954). (2) King, A., J . Chem. Sac. 1936, 1688. (3) Ibid., 1937, 1489. (4) Kistler, S. S., Fischer, E. A., Freeman, I. R., J. Am. Chem. Sac. 65, 1909 (1943’1. Kdlthoff, I. M., Ibid., 54,4473 (1932). Kruyt, H. R., de Kadt, G. S., Kallaid 2.47, 44 (1929). Lepin, L., Physik. 2. Sowjetunion 4, 282 (1933). Schilov, N., Shatunovska, H., Z . Physik. Chem., A150, 31 (1930). Schilov. N.. Shatunovska. H.. Chmutov, K., ibid., A149, 21’1 (1’930). Weller, S.: Young, T. F., J . Am. Chem. Sac. 70,4155 (1948). Wilson, J. H., Bolam, T. R., J . CalloidSci. 5, 550 (1950).
RECEIVED for review October 25, 1957 ACCEPTEDJanuary 9, 1958
Cor rect ions Hydraulically Driven Pumps The article, “Hydraulically Driven Pumps,” by D. H. Newhall [IND.ENG. CHEM.49, 1949 (1957)l has several discrepancies. I n Figure 1, the first portion of the sub-
INDUSTRIAL A N D ENGINEERING CHEMISTRY
caption following “Neglecting friction,”
a and p should not be subscripts but Pa = A p The subcaption P should read:
Low pressure piston of area, A Figure 3 caption should read: This double-acting pump, including low pressure system, gives essentially a continuous uniform flow except for crossover of valves (Figure 8,B).
On page 1953. Figure 7 , A should be inserted before The scheme and B before The hydraulic circuit.
On page 1954, Figure 8,A and B should be inserted before Single-acting pump and Double-acting pump, respectively. I n Figure 9, the diagonal lines should have the following figures added to the end of their lines. DA 7 should have 10 DA 4 should have 5
A New High Pressure Technique In the article on “A New High Pressure Technique” by D. H. Newhall [IND.ENG. CHEW 49, 1991 (1957)J the caption to Figure 2 should read: Simple free piston gage, calibrating a Bourdon gage I n Figure 3, the arrow from C should not point to the packing ring but to the re-entrant cylinder just below it.
Analysis of Porous Thermal Insulating Materials I n the correspondence on this subject [IND.ENG. CHEM.49, 1936 (November 19 57) ] misprints have caused two parts to be confusing. The correct versions are given below. The first sentence in the note of D. A. de Vries should read : An article on the heat transfer in porous thermal insulating materials was published by Topper (70). The last par1 of L. Topper’s reply should read: Using his symbols, when E ~ / E O is 0.1, Equation 4 gives E / E O = 0.49, while de = 0.47. Vries’ Table I1 gives E , / Q (de Vries states that-differences between the formulas proposed by me and Topper’s formula increase with increasing difference of B ~ / E S from 1, in particular for el/eO > 1. The small difference in the sample given by Topper is therefore not a t all surprising.)
