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INDUSTRIAL AQVDENGINEERING CHEMISTRY
nated chlorine will materially reduce any influence of neutral chloride in regard to alterations in the cationic complexes. Marked colloidality of the 33 per cent acid liquor containing large amounts of sodium chloride was evident. Concentrated solutions of the same chromic chloride gave no marked indication of colloidality. Therefore, the aggregation changes in this case are probably of most importance, and the decrease in tanning action of these colloidal e!ectrolytes containing great molalities of sodium chloride is probably due to too great agglomeration of the colloidal micelles. From this viewpoint optimum chargc: secondary valency activity, and colloidality of the chromic salt seem possible. The view of the formation of colloidal products as a requisite for chrome tanning agents is, however, untenable in view of the data presented in the experiments with the 86 per cent liquor. In this instance any formation of products of colloidal dispersities seems very improbable. The constitutional factor no doubt plays the primary role here, whereas in extremely basic liquors the degree of aggregation of the chrome complex and the colloidal influence of salt enter as additional factors. The reversal in tanning properties of solutions of chromic chlorides of normal acidities on the one hand and the extremely basic ones on the other hand, upon aging, although in both instances the hydrogen-ion concent,ration is decreased upon standing, gives further indication that the p H factor in chrome tanning is only a secondary and circumstantial function. Instead, the data point to the importance of structural, and therefore colloidal, changes of the chromic salt. From the ampholytic concept of hide protein it follows that the amount of ionized acidic protein group8 should decrease with increa5e in hydiogen-ion concentration. The decrease in fixation of chromium from chromic sulfates in the presence of common salt is considered by Wilson to be due in part to the hydration effect of the neutral salt upon chromic ions. Thus, indirectly the decrease in chrome fixation should depend upon the diminished activation of the protein caused
Vol. 19, No. 9
by the decrease in pH due to the addition of salt. This view is based on the assumption that the hide protein possesres the same number of free acidic and basic groups independent of the hydrogen-ion concentration, which probably is not true. Considering the hide pomdec in the vicinity of the isoelectric point to consist, a t least partly, of internally compensated structures, it would instead be expected that increase in hydrogen ion to a certain extent would manifest itself in an increase in the number of free acidic protein groups although their ionization would be less. According to this view, the influence of pH upon the protein should consist of two opposing reactions Increased chrome fixation should result from the opening up of the internal protein structure, due to increase in hydrogen ion, whereas the decrease in activation of free acidic protein groups by the decrease in pH would be expected to lead t o diminished reactivity of the protein for chromic ion. The relative magnitude of these opposing influences is probably controlled largely by the nature of the chromic salt and the hide protein This complicated influence of hydrogen ion is not readily conceivable in the system under consideration on account of the predominance of the constitutional influence of the chromic salt. In tanning practice the osmotic and similar effects of the neutral salt upon the hide and its attendant degree of swelling very likely influence the tanning process. ConcIusion
As previously pointed out, our present concept of the neutral salt effect in tanning is rather inadequate. The main finding of this investigation is that the degree of chrome fixation is not regulated by the hydrogen-ion concentration, but largely by the constitution of the chromic salt. It is hoped that the investigation of the nature of chromic salt which Professor Stiasny12 is now carrying out will also greatly extend our knowledge of this important problem. 12
Collegium, No. 671, 408 (1926).
Combustion Tray for Determination of Heating Value of Coal’ By Geo. B. Watkins and J. V. Hunn DEPARTMENT OF CHEMICAL ENGINEERING, UNIVERSITYOF MICHIGAN,ANN ARBOR,MICH.
T
HE annoyance of having a part of the coal sample blow from the combustion tray is familiar to all experienced in estimating the calorific value of coals in the bomb calorimeter. This difficulty has been overcome by using a type of combustion trav shown in Figure 1. The combustion tray is approximately twice as deep as the platinum or nickel tray ordinarily used. It was constructed from the cover of an illium crucible, of the type used for volatile matter determinations, by d r i l l i n g 0.159-cm. (l/le-inch) holes through the sides of the cover approximately 0.64 cm. inch) apart and 1 4 half way up. I I T h e u n b r i q u e t t e d coal sample is placed in the tray and heaped into the form of a cone. The loop of the iron fuse wire connecting the electrodes in the head of the bomb is bent down to 7/8 --/ touch the apex of the sample when Combustion Tray the tray is in position, As the combustion proceeds, oxygen is drawn in through the holes in the
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1
Received April 21, 1927.
tray, producing a baseburner effect and completely burning the coal sample. Coals having a high volatile content and high calorific value usually give the most trouble. Several parallel runs have been made on such coals using the ordinary type of nickel tray and the one described. The relative merits of these trays will be seen from the table, which shows the test runs made on a bituminous coal before satisfactory heating value checks were obtained. T a b l e I-Heating RUN
1 2 3 4 5 6 7
S 9 10 11 12 13
14
V a l u e Tests, S h o w i n g R e l a t i v e M e r i t s of T r a y s TRAY DESCRIBED NICKELTRAY Cal. Der gram Cal. Der gram Incomplete combustion” 7623 7563 Incomplete combustion 7596 Incomplete combustion 7628 Incomplete combustion Incomplete combustion 7604 Incomplete combustion Incomplete combustion Incomplete combustion 7580 Incomplete combustion
7617
Incomplete combustion
0 “Incomplete combustion“ refers t o test runs in which a part of the coal sample escaped combustion b y falling from the combustion t r a y durlng the burning period.
