INDUSTRIAL AND ENGINEERING CHEMISTRY
1320
It is obvious that the low-temperature distillation of wood in itself is of but little interest from the point of view of gas manufacture since, even if the large proportion of carbon dioxide could be removed, the low yields would offer an insuperable obstacle to economic production. Where large.scale production of either distillate or distillate and charcoal i s desirable, however, it is feasible to pass the low-temperature gas through a bed of incandescent charcoal in machines of either the blue gas or producer type and thereby, at the expense of an equivalent amount of charcoal, convert the carbon dioxide into carbon monoxide. If wood distillate alone is desired the whole of the charcoal can in these operations be converted into gas. If in a two-stage operation of this sort the low-temperature gas were passed through a blue gas machine, the effect would be not only to reduce carbon dioxide to carbon monoxide but also to lower the hydrocarbon content of the gas, the hydrogen content thereby undergoing a corresponding increase. The resulting product would resemble blue gas, and of course blue gas itself could be generated simultaneously, to any desired extent. Making reasonable assumptions as to conversion efficiencies, it is to be expected that as much as 25,000 cubic feet of gas having a heating value of approximately 300 B. t. u. could be obtained in addition to the wood distillate of the low-temperature carbonization by use of a ton of absolute wood substance. The alternative of passing the raw low-temperature gas through a charcoal producer should yield something like 40,000 cubic feet of product having a probable heating value of 180 €3. t. u. Because of lower operating costs and higher conversion efficiencies this procedure should offer economic advantages in any situation where gas of this quality could be used.
Vol. 18, No. 12
Value of Low-Temperature Distillation By-products
An evaluation of the by-products of low-temperature wood carbonization involves many variables. The charcoal obtained in low-temperature carbonization is usually in good demand a t prices considerably in advance of the cost of other forms of fuel and to the extent that it could be marketed a t good figures should not be gasified. The value of crude pyroligneous acid w ill be greater if it is produced from the usual hardwoods than if obtained from resinous woods. The crude distillate from Douglas fir contains but 30 per cent as much methanol and but 60 per cent as much acetic acid as that from hardwood. The profitable recovery of these substances from Douglas fir distillate by methods traditionally used in the industry is hardly to be expected. Substantial progress is being made with other methods, which in large-scale operations should produce attractive returns. Conclusions
In the foregoing cursory survey of the status of gas production from wood the outstanding fact is that the several methods of gas production which have been developed during the past century for use with coal, find really a close parallelism where wood is to be carbonized or gasified. Practice has demonstrated that thermal efficiencies in gasmaking operations involving these two materials are much the same. Each material has its peculiarities and these must be thoroughly understood before the technical details concerned in successful gas-making can be carried out. Vastly more has been done in the study of coal than has ever been attempted with wood, but in spite of this fact there is a sufficient accumulation of dependable experience to justify the assertion that in the field of manufacture of low B. t. u. gas the use of wood deserves much greater consideration than usually is accorded it.
Determination of Metallic Lead in Metallurgical Products and Pigments' By Donald H. McIntosh RESEARCHLABORATORIES OB UNIVERSITY OF UTAH,IN CO~PERATION WITH U. S. BUREAUOF MINES,INTERMOUNTAIN EXPERIMENT STATION, S A L T LAKECITY, UTAH
T
HE method described is the result of an investigation to find a means of determining the extent of the reduction of lead ores and concentrates after a treatment with the reducing agents commonly used in metallurgical practice. In order to obtain definite data it was necessary to devise an accurate method for determining the amount of bad that had been reduced to metal. The method, which is applicable to matte and slags, offers a means of determining the amount of metallic lead in these products and consequently will aid in determining the optimum settling conditions to be maintained in blast furnace practice. Where chemical processes that convert metallic lead into other forms are used, a method of determining how far that conversion has progressed will be of especial importance. Chemicals and Apparatus Sodium hydroxide solution, 50 cc. of 15 per cent, by weight 10 per cent silver nitrate solution, 10 cc. Concentrated sulfuric acid, 10 cc. 50 per cent alcohol solution, 15 cc. 1
Received June 19, 1926.
U. S.Bureau of Mines.
Published by permission of the Director,
Saturated ammonium acetate solution, 5 cc. Standard ammonium molybdate solution Tannic acid indicator solution Asbestos for Gooch filter Pyrex beaker (250 cc.) Erlenmeyer flask (250 cc.) Principle of Method
The properties of metallic lead upon which the method depends are its insolubility in sodium hydroxide solution and its solubility in silver nitrate solution. It was found by experiment that the silicate, carbonate, oxide, sulfate, and a part of the sulfide of lead were soluble in sodium hydroxide solution and could be removed by filtering, leaving a residue containing the metallic lead and the remainder of the lead sulfide. Under the conditions established as standard in the method, metallic lead is soluble and lead sulfide is insoluble in silver nitrate solution; consequently these two substances may be separated by treating with silver nitrate and filtering. The dissolved metallic lead in the filtrate may be determined by titrating with standard ammonium molybdate solution. After careful trial upon synthetic products the following procedure was found to give accurate results:
December, 1926
INDUSTRIAL A N D ENGINEERING CHEMISTRY Procedure
Place 1 to 10 grams of the sample in a 250-cc. beaker and add 50 cc. of a 15 per cent solution of sodium hydroxide and boil for 5 minutes. Filter through a thick asbestos mat on a Gooch crucible and wash thoroughly with hot water. N o l c T h e metallic lead, which is insoluble in sodium hydroxide, is oow on the filter together with the remainder of the sulfide, if this latter material was present in the sample. If much lead silicate is present some of it may be on the filter, but since the silicate is not attacked by silver nitrate in the subsequent treatment, its presence is immaterial.
Place the mat containing the residue in the original beaker and wash the crucible with about 10 cc. of 10 per cent silver nitrate solution, allowing the washings to mix with the mat and residue in the beaker. Break up the mat and residue by stirring vigorously with a glass rod for one minute. Wash down the sides of the beaker with a stream of cold water, using about 2 cc. in order to avoid dilution of the silver nitrate solution. Repeat the agitation and filter the mixture on another Gooch crucible, containing a thick mat of asbestos, into an Erlenmeyer flask washing the residue thoroughly with water. (The metallic lead is in solution while any of the other lead compounds that are insoluble in sodium hydroxide remain on the filter.) To the clear filtrate in the flask add 10 cc. of strong sulfuric acid and evaporate to fumes. Cool the flask, dilute the solution with 50 cc. of distilled water, and boil. Filter off the lead sulfate on a tight filter paper, wash thoroughly with a 50 per cent solution of alcohol and t,hen once with cold water. Put the filter paper containing the lead sulfate in the flask, and dissolve the lead with 10 cc. of a hot saturated solution of ammonium acetate. When solution is complete, dilute with distilled water to 250 cc. Boil and titrate with a standard solution of ammonium molybdate, using tannic acid as an indicator.
1321
If much metallic lead is present it may be necessary to weigh the sample and to dilute it with a weighed amount of lead-free material, such as quartz, which will assist in abrading the malleable metal. The per cent of metallic lead in the original sample may be calculated from the results of the determination and the weights of the original sample and the diluent, as follows: Let S = weight of original sample D = weight of diluent p = per cent of metal in total sample M = per cent of metal in original sample M = - P(S S P(1 Then
+m
~
+);
Notes on the Method
This method will give excellent results on finely divided lead and interference by other materials likely to be present in the sample has been found to be negligible. The presence of other metals in the sample which are insoluble in sodium hydroxide, but are dissolved by silver nitrate, requires the use of additional silver nitrate. Filter paper cannot be used in place of the Gooch crucible and asbestos, because of the reaction between the paper and the sodium hydroxide. The amphibole variety of asbestos is superior to the other types because of its stiff fine texture which allows clean filtration upon a comparatively thin mat, Close timing of the treatment with silver nitrate is not essential unless extreme accuracy is desired. The action of the silver nifrate upon the metallic lead is rapid. Undulg prolonging the time of contact results in dissolving a small amount of lead sulfide when this substance is present. The molybdate solution should be standardized against pure metallic lead by dissolving with silver nitrate and treating as described for the regular determination. If small deviations from the correct results are immaterial the method may be shortened considerably as follows:
Grind the sample containing the metallic lead on a smooth bucking board to pass a 75-mesh sieve, being careful to take up any metallic lead that adheres to the board by scouring the smooth surface with some of the first material to go through the sieve.
After filtering the solution, following the dissolving of the metallic lead by silver nitrate, sulfuric acid may be added to the clear filtrate and the solution heated to boiling. The precipitated lead may then be filtered offand treated as directed in the regular procedure. In this way the loss of time required to evaporate the solution t o fumes may be avoided.
Ascarite as C02 Absorbent' By J. S. Buck DUKEUNIVERSITY, DURHAM, N. C.
OR some time the writ,er has been using ascarite for carbon dioxide absorption in carbon-hydrogen determinations.2 The material is very satisfactory for this purpose, as it is solid, is readily replaced, does not give up water easily, and requires no previous saturation with oxygen. It permits of more rapid combustions and the change of color indicates the degree of exhaustion. The absorption tubes are readily constructed from 15 X 150-mm., thin, rimless Pyrex test tubes. The calcium chloride tube weighs about 25 grams and the ascarite tube 40 to 45 grams when charged. They are closed by marked rubber 'caps, and a small (unweighed) calcium chloride guard tube is attached during the combustion. The light weight, small surface, mechanical construction, and large capacity permit rapid work. One-tenth gram is a suitable amount for analysis, and a combustion tube 9 mm. internal diameter is recommended. The use of several tubes in rotation increases-the speed of 1 Received
t
July 12, 1926. See also Marsh, J . Asroc. Oficial A n . Chcm., 8, 442 (1925).
Shaded? parts are: glass wool a a .L
CaCl2
0 a
e
v)
