146
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
first fill t h e filter body with a very t h i n slurry of carbonate of lime a n d filter this mixture for a few seconds until a film of lime, s a y l / 8 2 inch in thickness, has been deposited. This coats t h e cloth as completely and evenly a s a deposit could possibly be made. T h e lime slurry is t h e n drained off a n d filtration commenced. T h e coating of lime forms a complete film between t h e cloth a n d gummy residue, so t h e latter never even touches t h e cloth. When ready t o clean t h e cloth t h e reversal of current is effective because t h e coating of lime breaks away readily. It is frequently asked how we can tell when cakes of sufficient thickness have been formed, especially when t h e material filters a n d builds up t h e cake rapidly. This is not as difficult as would be imagined. T h e usual way is t o work a t a given pressure, say forty pounds per square inch, a n d p u m p for a certain number of minutes, determined b y practice t o form t h e required cake. Another way is t o p u m p a certain number of inches from t h e supply t a n k for each charge. As in all processes, t h e operative soon becomes expert, a n d can iudge from t h e general conduct of t h e filter when t h e charge is sufficient. T h e usual skepticism which attends t h e introduction of a n y new machine was encountered a t first, b u t so many installations are now in successful use a s t o establish fully t h e usefulness of t h e methods described. A noteworthy point is t h e fact t h a t many of t h e filters of this t y p e i n use are of much larger size a n d capacity t h a n i t is found practicable t o build filter presses. Many have been built with a capacity of 133 cubic feet of cake per charge a n d several others ranging from 80 t o 1 2 0 cubic feet per charge. One especially large one was built which dumps over z j tons of cake per charge. T h a t this apparatus is now far beyond t h e experimental stages is demonstrated by t h e fact t h a t a large beet sugar factory in California installed three large hydraulically operated machines for t h e 1913 campaign. They were installed almost a t t h e last minute before t h e campaign started and were a t once placed in service a t full capacity, a n d no difficulty was encountered, in spite of t h e fact t h a t none of t h e employees who operated t h e machines had ever seen one before. T h e time required t o open, clean a n d close one of these filters is about five minutes, which minimizes labor t o such a n extent t h a t one operator can t a k e care of several large machines, even though each machine has t o be cleaned hourly.
Vol. 6 , No.
2
in a deep trench, a n d after lining this shell with firebrick a n d mineral wool and stopping t h e ends with 13-inch brick walls, it was covered with two feet’ of earth. The chamber was constructed so as t o be as
SIDE VIEW OF “COMBUSTION OF COAL”APPARATUS
nearly air-tight as possible, a n d in such manner as t o retain t o t h e greatest degree practicable a n y heat generated within its walls. A t one end a motor-driven f a n will blow in air a t a r a t e which can be accurately measured, a n d a t t h e other a stack is provided which can be opened or closed a s desired. Through t h e top of t h e chamber, a t frequent intervals, pass small pipes for withdrawing samples of air or gases a n d for inserting pyrometers for temperature measurement in the interior. The chamber will hold 6 t o 8 tons of coal when onethird full. It is expected t h a t different kinds of coal or of t h e gob or waste material from mines will be placed in t h e chamber a n d a s t u d y made of spontaneous development of heat in t h e m under various conditions. After a n active fire has been started in t h e chamber
SWEETLAND FILTERPRESSCo. 149 BROADWAY, NEW Y O R K
IMPROVISED MINE FIRES ON AN EXPERIMENTAL SCALE Received January 15, 1914
T h e Bureau of Mines has recently installed a t its Pittsburgh experiment station a n underground chamber or furnace in which t o carry on experiments relating t o mine fires a n d spontaneous combustion as occurring in mines. A section of steel t u b e cylindrical in shape, 6l/2 feet in diameter a n d 2 7 feet long, was laid on its side
CROSS SECTION OF “COMBUSTION O F COAL” APPARATUS SHOWINQ METHODOF COXSTRUCTION O F BRICKLINING
either by this means or artificially, experiments will be made on controlling t h e fire b y reducing t h e air supply or b y sealing it off entirely. T h e progressive changes in composition of t h e fire gases or of t h e air surrounding t h e coal will be followed a n d temperature measurements made, in a n endeavor t o apply t h e d a t a
Feb., 1914
T H E J O U R N A L OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
t h u s obtained t o solving practical problems in t h e t r e a t m e n t of mine fires. Investigations have been made in other countries a n d t o some extent also in this Country, of t h e gases produced in actual cases of mine fires both before a n d after sealing off n burning area. T h e bureau is now making, however, probably t h e first a t t e m p t t o in-
“COMBCSTIOS
OF COAL”
.kPPARATUS S H O W I N G G A S A N D A I R
f47
t y p e of shaker used b y t h e writer a n d believed t o have certain advantages. DESCRIPT1Ox.-The principle is as follows: T h e bottles with soil a n d water are ended over a n d over, t h u s allowing t h e contents t o fall from one end of t h e bottle t o t h e other. This is accomplished b y having t h e bottles attached radially t o a wheel which is rotated slowly in a vertical plane. T h e machine used b y t h e writer is “home-made” a n d consists of t w o small cart wheels sixteen inches in diameter, both on t h e same axle a n d touching h u b t o h u b : this leaves t h e edges of t h e tires about three inches a p a r t . Strips of t i n fastened t o t h e fellies serve n o t only t o hold t h e t w o wheels together, b u t also with t h e fellies act as a broad groove ( I ~ / zinches wide) for a belt t o r u n on. T h e bottles used are t h e kind known commercially as “four ounce sample oil bottles:” t h e y are about six inches long a n d one a n d one-half inches in diameter, a n d are fitted with rubber stoppers: t h e y have a capaci t y of 1 2 0 cc. T h e base of each is slipped into a sleeve of tin fastened near t h e h u b : a mire clamp secures t h e bottle a t t h e neck. T h e wheel t h u s constructed will hold sixteen of these bottles arranged radially-eight on a side. I t m a y be attached t o a motor b y means of a belt. Plate I is a photograph of t h e machine.
CONXfiC
T I O N S TO C O X B C S T I O i Y C I I A X B E R
vestigate such problems in a n experimental a p p a r a t u s which permits careful control of conditions a n d yet is on a scale nearly commensurate v-ith mining operations. These investigations are being carried on by Horace C . Porter. chemist, of t h e Bureau of l i i n e s . A S H A K E R F O R T H E MECHANICAL ANALYSIS O F S O I L By FREZMAS \YARD
Recei\.ed October 2 3 , 1913
IsTRoDvcToRy..-In t h e mechanical analysis of soil one of t h e prime requisites is t h e complete separation of all t h e particles before sorting t h e m into groups or grades according t o size. T h e tendency in t h e natural soil is for t h e finer particles either t o gather among themselves as aggregates or t o cling t o t h e larger grains. If a complete separation is n o t effected t h e per cent of t h e finer grades of soil will be below, a n d t h a t of t h e coarser grades above t h e t r u t h . T h e separation can be effected mechanically in one of t w o ways---pestling a n d stirring; or shaking, as advocated b y t h e Department of Agriculture*-water (very slightly ammoniacal) being added in either case. T h e essential idea of t h e latter is t o place bottles containing soil a n d water i n a horizontal position in t r a y s which are jerked backward a n d forward by means of a n eccentric a t t a c h m e n t . T h e purpose of this article is t o describe a different C. C. Fletcher and H. Bryan, “Modification of the Method of Mechanical Soil Analysis,” U. S. Dept. Agr., Bur. Soils, Bull. 84, 1912.
PLATE I
T o operate-put weighed ( I O grams) sample of soil i n bottle; fill one-half full of water which is slightly ammoniacal; a t t a c h bottle t o wheel a n d revolve a t t h e r a t e of twenty-five revolutions a minute; let r u n for three hours. ADVAr;TAGEs.-Separation by stirring and pestling is too laborious, consumes too much time, does not always result in a clean separation a n d has a tendency t o mechanically fracture t h e particles of soil. Both t h e shaker methods are not only safer, a n d more effective, b u t , since t h e y can be r u n b y machinery, are convenient. And in either case t h e removal of t h e grades silt a n d clay by sedimentation a n d decantation
