« AnteriorContinuar »
NOTE ON DETERMINING LOSS OF ALKALI IN LIME SLUDGE FROM CAUSTIC SODA.
By ROBERT E. DIVINE.
When testing lime for quicklime content, make a test on an aliquot representing 2 grams of the original lime by adding an excess of ammonium carbonate solution and evaporating to dryness on the steam bath. Record percentage increase of weight. Treat a sample of wet mud in the same way, and after weighing, wash with water and titrate the filtrate with N/4 acid and methyl orange. Deduct the weight of alkali from that of the dry carbonated mud, and calculate weight of original lime from the figure found above for percentage increase when original lime is carbonated. Knowing the ratio between quicklime and soda ash used in the causticisers, the actual percentage loss of alkali is a matter of simple calculation.
Suppose a preliminary carbonating test on lime gave an increase to 163%, and that the dry carbonated mud weighed 1.725 grams; that the filtrate containing alkali required 0.6 c.c. N/4 acid; that the proportions of lime and soda ash used in causticiser are 72 pts. lime to 100 pts. ash. 1.725 0.008 (alkali) = 1.717 dry carbonated lime.
0.0081.053 = 0.0076 pts. alkali for 1 pt. lime and for 72 pts. lime or 100 pts. soda ash there is 72 X .0076 0.547 alkali, which represents, practically, the percentage loss on a high grade ash, and from which the loss on a low grade ash may be calculated.
Too much phosphorus in a phosphor-bronze bearing causes the tin to liquidate in the form of "tin-spots" which are nearly as hard as steel. Such "tin-spots" cut the axle and cause the bearing to heat.
For the 11 months ending with November, 1907, the imports of platinum into the United States were 5,726 lbs., valued at $2,337,519, as against 10,561 lbs., $3,229,935, in 1906. The falling off for 1907 was equivalent to 4,835 lbs., or $892,416. There is no import duty on platinum.
Consul F. W. Mahin, of Nottingham, reports that the manufacture of aluminum cables as electric conductors in place of copper has actively begun in Great Britain. The cables and wires being made there are covered with vulcanized bitumen treated by patented methods, and they are, it is claimed, not brittle at low temperatures nor unduly soft at the high temperatures to which they would be subjected in ordinary use.
THE DUST EXPLOSIONS AT MINNEAPOLIS MAY 2, 1878,
AND OTHER DUST EXPLOSIONS.
By S. F. PECKHAM.
The occurrence at long intervals of time, of terrific explosions, attributed to the ignition of mixtures of oxidizable dust and air, too frequently calls the attention of scientific men to the origin and prevention of such disasters.
It is for the purpose of making a permanent contribution to the literature of this subject, that the following reports are offered, which, while made nearly thirty years ago, have never been printed in any scientific journal. As the reports were made to a coroner's jury, it was claimed at the time, through local influences, that they were the property of their authors no longer, after they were delivered to the coroner, hence the authors had no right to publish them, such right having passed to the county under which the jury acted. As a result, the reports were never published, except in the local papers.
As frequent requests have been made, as occasion has brought the subject of Dust Explosions under discussion, for copies of these reports, all of which have of necessity been refused, I have concluded to publish the reports, verbatim, as given to the jury, with the verdict of the jury, and such conclusions as the present aspect of the subject warrants.
As I was sitting at the tea-table on the evening of May 2, 1878, I was startled by a noise as if a barrel of flour had been tipped over on the floor above. In a moment the sound was repeated. We all rushed to the door from which could be seen the flouring mills of the city, about a mile distant. A column of black smoke arose to a great height above the spot where the largest mill and an elevator had stood, and spreading out like an immense mushroom, it floated off with the wind, which was blowing from the large Washburn A mill towards the Diamond and Humboldt mills, they being directly behind the elevator from where I stood. The elevator, 108 feet high, was wrapped in flames from sill to ridge pole; if it had been drenched with oil it could not have ignited more quickly. Immediately after, flames were pouring from every window in the three mills to windward, standing on the bank of the river, which were wholly consumed but did not explode. Six flouring mills, the elevator, a machine shop, blacksmith's shop and planing mill, with a number of empty and loaded cars, were in flames in five minutes from the time fire was first observed by any one who survived the disaster, producing a conflagration, that, from ordinary causes would not have gained such headway in two hours.
At the instant the Washburn A mill exploded, all observers agreed that
the mill was brilliantly lighted from basement to attic. One witness, who was crossing a bridge that spanned the Mississippi river, below the mills, had his attention called to, what he described as a stream of fire, which issued from one of the basement windows and went back again. Immediately thereafter each floor above the basement became brilliantly illuminated, the light appearing simultaneously at the windows as the stories ignited one above the other. Then the windows burst out, the walls cracked between the windows and fell, and the roof was projected into the air to a great height, followed by a cloud of black smoke, through which brilliant flashes resembling lightning passed to and fro.
An examination of the ruins showed that the walls of the Humboldt mill lay upon those of the Diamond mill, and those of the Diamond mil! upon those of the west end of the Washburn A mill; showing that they exploded successively. The Washburn A mill evidently exploded from a fire originating within it, the high wind carrying the flame into the mills adjoining to the south, while there was enough burning middlings projected through the broken windows of the mills to windward to set them on fire; but they did not explode. The three mills that exploded were running, those that did not explode had been shut down for several days.
No proof was offered that any explosive material other than is produced in the manufacture of flour from wheat, was in any one of the buildings destroyed, in the cars around them or in the neighborhood. No suspicion of incendiarism was expressed.
Eighteen men were killed in the several buildings.
A coroner's jury was empaneled to investigate the cause of their death, which consisted of some of the most intelligent men in the community. The jury organized, and immediately requested Prof. Louis W. Peck, then in charge of the Department of Physics in the University of Minnesota, and myself, who then held the chair of chemistry, to sit with the jury and question the witnesses as we saw fit. This we did.
As Prof. Peck was a trained mechanical engineer and I had very little experience in such subjects, it was agreed between us, that he should confine himself to the mechanical and physical problems presented, while I should consider only the chemical problems.
We were also requested by the jury to confine any discussion that we might present to the jury in the form of reports or otherwise, to the evidence given in this case and to any experiments that we chose to make which would explain or render such evidence clearer.
After the evidence was all in the jury met in the chemical lecture room of the University of Minnesota, and the following report was read by PROF. LOUIS. W. PECK:
RESULTS OF EXPERIMENTS
upon the following materials:
6. General dust from mill-that is from beams, etc.
7. Dust from middlings machines.
Dust from flour dust house (from stones). 9. Flour.
ATTEMPTS TO BURN IN BULK.
A small amount of each of the above was placed in separate piles upon a board, and the flame of a Bunsen's gas burner directed against them.
In each case, excepting the wheat dust, the material gave a little blaze lasting from one to four seconds, after holding the blaze against it for half a minute, but after holding the jet against it for five minutes it would leave a charred surface and no blaze.
With wheat dust the blaze at first was a little larger, but it would soon go out upon removing the gas jet; unlike the other materials, however, it would retain glowing coals. These coals could not be made to blaze by fanning, but they communicated a fire to the wood which by careful blowing was made to blaze.
All of the substances form such a compact mass when in bulk that it does not seem possible to make them burn under the most favorable circumstances from heating upon the outer surface; when thrown upon the light in a body they put it out.
RESULTS OF BLOWING THE ABOVE MENTIONED MATERIALS INTO THE AIR BY
BELLOWS OVER A GAS FLAME. (Fig. 1.)
Coarse bran would not burn. Fine bran and flour dust burn quickly with considerable blaze. Middlings burn quicker but with less flame..
All the other substances burn very quickly, very much like gunpowder. All the materials except the coarse bran burn with explosive rapidity under the above circumstances.
In all these cases there was a space around the flash where the dust was not thick enough to ignite from particle to particle, hence it remained in the air after the explosion. [NOTE-An explosion is a bursting, usually with a report. We speak of gunpowder as an explosive, that is when the proper chemical action takes place between its different parts, gases at a high temperature are produced which require a very great additional space, hence the bursting. Coal gas and air when mixed and caused to unite produce a gas at a high temperature which require an additional space, hence the bursting. Flour dust, flour middlings, etc., when mixed with air, thick enough to ignite from particle to particle and separated so that each particle is surrounded by air, will unite with the oxygen in the air producing a gas at a high temperature, which requires an additional space, hence the bursting].
Flour is an explosive just as powder and coal gas are explosives, but in all cases it is the gas produced which causes the bursting.
There is no gas which comes from flour or middlings that is an explosive; it is the direct combination with the air that produces gas requiring additional space. Powerful electrical sparks from the electric machine and from the Leyden jar were passed through the air filled with dust of the different kinds, but without an explosion in any case. A platinum wire kept at a white heat by a galvanic battery would not produce an explosion. The dust would collect upon it and char to black coals, but would not blaze nor explode.
A piece of glowing charcoal, kept hot by the bellows, would not produce explosion when surrounded by dust, but when fanned into a blaze the explosion followed. A common kerosene lantern when surrounded by dust of all degrees of density would not produce an explosion, but when the dust.
was blown into the bottom through the globe and out of the top it would ignite.
EXPLOSION IN ENCLOSED SPACE.
A strong wooden box of 1 15-16 cubic feet capacity with a heavy loose cover 12 x 18 inches was used first.
A hole was made in one of the lower corners for the nozzle of a pair of bellows; the experiment was tried of placing a handful of any of the above materials, excepting coarse bran, in the corner of said box, placing an uncovered lamp therein, the cover being upon the box with two men standing