May, 1925
I S D C ' S T R I A L B.1-D ESGISEERIA-G CHEMISTRY
burned, soinetinics in an electric tube furnace and sometiines in the laboratory rotary kiln. The effect of the sulfate group alone was determined on samples burned in an atmosphere containing sulfur dioxide, and also by additions of calcium sulfate and ammonium sulfate before burning. Sulfides were introduced by burning in a reducing atmosphere. The effect of sodium salts was tested by the addition of chloride, nitrate. and carbonate, as well as sulfate. When the tube furnace was used the materials were ground intimately together dry, and were also sometimes ground wet to obtain a more intimate mixture and one more comparable with the sludges. Materials to be burned in the rotary kiln mere $1ways mixed wet and made into small cubes to avoid excessive loss of dust from the kiln. of H y d r a t i o n of Lime as Affected hy A d d i t i o n s of K n o w n S u b s t a n c e s hefore B u r n i n g Time required for maximum rise of temDuration MATERIAL ADDED. CALCD PPTD. C A C O ~ of burning A S PERCENT OF BURNEDLIME peratures PLUST H E Acid Base Minutes FOLLOWING Hours .4--Samp!es burned i n small elec2rrc lube j u r n a c e a1 900' C. N o addition 1 1 1.5 1 2 2.0 . 1 2 1 1 . 4 CaO 2.7 3 1 1 4 CaO 2.7 Ca(NO&, dry 1 1 . 4 CaO 3.5 2.0 CaSOI, dry 7.0 0.69 0 60 NazO 1 NaCl soh. 7 0 4.33 SO? gas, 1% 3 1 , 5 6 NazO 20.5 1 2.0 NazSO4, dry 34 1 . 5 6 NazO 2.0 1 NazSOI soln. 2 . 1 6 Nap0 3.76 1 N a N 0 3 soln. 2 , 1 6 NalO 3.76 1 N a N 0 3 , dry C. T i m e in k i l n , 30 tninules B-Burned i n laboratory i'olayy kiln 1 0.5 N o addition 0.35 0 . .5 NazO 6 0.5 NazC03 1 . 0 Na20 11 0.7 0.5 NazCOs 1 . 5 Nan0 li 0.5 1. 0 NazC03 1 . 5 6 NaiO 17 0.5 2.0 NazSOd" 2 . 0 NazO 20 1.4 0.5 NazCOa 2 . 5 Nan0 21 1.7 0 5 NazCOs 3 . 0 NazO 15 2.1 0 5 NazCOa 24 -3. j 3 5 NarO 0.5 NazCOs a Mixture burned in reducing atmosphere in limekiln so that over half total sulfur was in sulfide form. T a b l e 111-Rate
2
ing action on the hydration and he also lihted barium and aluminium chlorides as accelerating agents. He I eported sodium chloride, lithium chlol-ide, potasiium bicarbonate, potassium nitrate, ammonium hydroxide and calcium hydroxide as indifferent, and potassium hydroxide, sodium hydroxide, potassium bichromate, and boric acid as agents retarding hydration. Rohland's technic differed considerably from that of the writers in that he added so little mater that the resulting product was a dry powder. He does not give any quantitative figures as to retardation, but merely indicates the direction of the effect. Seither Rohland nor Candlot included sodium sulfate in the list of salts tested. Kohlschutter and Ralther3 studied the effect of dissolved salts on the rate of sedimentation of lime hydrated in a rather large volume of water, but did not make any observations on the rate of hydration, merely noting that the rise in temperature \vas slight and soon equalized itself. In the work in this laboratory only qualitative observation was made on the rate of settling, but all the limes containing sulfates settled rapidly. The effect of nitrates was not consistent. At least one sample to which calcium nitrate had been added before burning settled extraordinarily slowly. Conclusion
The experimental work shows that sodium salts present in lime sludges retard the rate of hydration of the lime burned from these sludges. The acid radicals SOs and KO3 introduced as sulfur dioxide, ammonium sulfate, calcium sulfate, and calcium nitrate exert little effect. Sodium salts introduced as chloride, sulfate, nitrate, and carbonate exert ail influence roughly in proportion to the amount of S a z Opresent, provided burning conditions are the same. The addition of 2.0 per cent Na20 to a precipitated calcium carbonate changes the resultant lime so that it hydrates in 20 to 40 minutes instead of in 1 minute. A11 the limes containing sodium sulfate yield hydrates that settle rapidly. 3
The data given in Table I11 are divided into two groups in accordance with the method of burning. It v;ill be noted that the temperatures in the two kilns were kept as closely a t 900" C. as feasible, but that the duration of heating was twice as long in the tube furnace. There is no appreciable difference in the rates of hydration of pure lime in the two series, the maximum temperature being reached in every case by the end of the first minute. The addition of sulfate radicals alone by the use of sulfur dioxide or ammonium sulfate or calcium sulfate has a rather small retarding influence. So also the nitrate group when added as calcium nitrate has little effect. Sodium salts, however, exert a marked influence, which seems to be roughly independent of the nature of the acid radical and to be more a function of the quantity of S a n Opresent. The samples burned for an hour in the electric tube furnace are affected much more strongly than those from the rotary kiln, whose hot zone was kept as closely as possible a t the same temperature as the tube furnace but with the total time in the kiln only half as long. The influence of sodium sulfide as distinct from sodium sulfate was studied in one case by burning the mixture in a lime kiln with a strongly reducing atmosphere, so that over half of the total sulfur was in the sufilde state. The test on this lime is given in the fifth line of the second group Table 111. It apparently comes in its proper place for its percentage of S a 2 0 , with no visible effect due to the sulfide group. The hydration of lime has been studied by Rohland,z who tested the effect of soluble salts dissolved in the water in which the lime was hydrated. He confirmed Candlot's earlier work that calcium chloride eserted a strong accelerat. 2
Z a n o r g Chem , 21, 28 (1899).
521
Z Eleklrochem., 26,
159 (1919)
Amalgamating Metal Used in Molding Asphalt' By L. J. Catlin THES T A N D A R D
OIL
c0. ( K A N S A S ) ,
h'EODESHA,
KANS.
preparing asphalt for certain tests it can be poured hot ItheNinto molds and will not adhere to the metal surface when mold is removed if the surface to which the asphalt is adjacent has been amalgamated thoroughly before using. The following method has been found rapid and very satisfactory for spreading a film of amalgam on the surface of copper or brass: Thoroughly clean the surface to be anialgamated and then immerse in a solution of mercury bisulfate. The solution lasts longer and amalgamation is more rapid if free mercury is added and the metal brought in contact with the free mercury under the bisulfate solution. This may be kept in stock in this form and be ready for immediate use xhen desired. If the bisulfate is not a t hand, use diluted sulfuric or hydrochloric acid over the mercury, it being merely necessary to have present a negative radical which will allow the mercury to displace the metal to which it is electronegative. This brings clean mercury into contact with clean metal and an amalgam is soon formed which will carry an adherent film of free mercury. 1
Received March 31, 1928
