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kymograph was started by means of a n electromagnetic device, so t h a t the only contact of the suspension with the building (other t h a n its overhead supports) was through a spiral of fine copper wire. The curves obtained are shown in 0 and P. A comparison of these curves with t h e others shows t h a t a spring suspension is markedly superior t o a n y of t h e supporting devices developed. Considerable vertical vibration is still present, however, and a photomicrographic apparatus mounted on this suspension did not give uniformly satisfactory results, even a t low magnifications. The results obtained with a combination of t h e supporting device (Fig. 3 4 and t h e suspension, i. e., tetrahedra placed under t h e vibration instrument on the frarnework of t h e suspension, are shown in Curve Q. This curve shows considerable improvement, and the arrangement is very little mqre unstable and awkward t h a n the suspension alone. I n conclusion, we wish t o point out t h a t every laboratory vibration problem must be solved independently, because freedom from vibration a n d great stability are not reconcilable. The determining factor is, of course, the degree of freedom from vibration t h a t is required, and this being once fixed determines the amount of stability possible. T h a t is, a mounting of great stability can be constructed which would be entirely satisfactory for a quantitative balance, but for high-power microscopic work greater freedom from vibration is required and hence less stability can be obtained. For very sensitive instruments such as galvanometers, where the greatest freedom from vibration is required, lack of stability must be accepted as a necessary evil. T h e devices which have been found effective in absorbing vibration may be arranged in the order of their merit as follows: I S p r i n g suspension n-Tetrahedron arrangement of rubber balls 3-Balls separated and held by a wooden frame 4-Air bags inflated at from z to 5 Ibs. pressure
The second of these has been used in this laboratory with complete success as a support for a Leeds a n d Northrup reflecting galvanometer, type 2420, quantitative balances, and high-power microscopes. SUMMARY
A simple apparatus for making comparative measurements of vibration has been constructed. T h e results of measurements of the vibration absorbing capacities of various devices are presented. Certain arrangements of rubber balls have been found very effective. The Federal Trade Commission has cited the United States Refining Company of Cleveland, Ohio, in complaint of unfair competition in the manufacture and sale of paints and other products. The complaint alleges false and deceptive advertising. At a recent meeting of the Gypsum Industries Association, six to eight fellowships were provided for, each with a stipend of $1000 to $1500 a year, to be located a t various agricultural colleges in the eastern United States, for the purpose of investigating the use of gypsum in crop production and for making a fundamental study of the relation of sulfur to crop nutrition and growth.
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WATER SOFTENING FOR THE MANUFACTURE OF RAW WATER ICE1 By A. S. Behrman INTERNATIONAL FILTER Co., CRICAGO, ILLINOIS
The manufacture of ice from distilled water is rapidly being replaced by the production of ice from raw water -or, more strictly speaking, from undistilled water. The two agencies principally responsible for this development are cheap, dependable power and applied chemistry, in the form of water softening. The requisite characteristics of first-quality ice are clearness, firmness, and freedom from discoloration. These qualities are possessed by ice made from pure water, free from dissolved solids and gases, such as t h e reboiled distilled water which has, until comparatively recently, been almost exclusively used in the artificial ice industry. Ice frozen from impure water is opaque, discolored, or brittle, depending on the nature of the impurities. Freezing water is, in many respects, much like boiling and evaporating it, in t h a t by far the greatest part of the substances dissolved in t h e water freeze out in the ice made from it. T h e most effective purification of raw water for ice making is, therefope, t h a t which reduces the objectionable impurities in the water t o a minimum. It is now generally recognized t h a t this most effective purification is accomplished by lime-soda softening, followed b y sand filtration. METHOD O F MANUFACTURE O F R A W WATER
ICE
I n the process of manufacturing ice from raw water, cans of the water are surrounded by a sodium or calcium chloride brine having a temperature usually 1 2 ” t o 18” F. Air, under either high pressure (15 t o 25 lbs.) or low pressure (3 t o 5 lbs.), is bubbled through the water as i t freezes, t h e high-pressure air being in general more effective. The first ice formed around t h e sides of a can is usually relatively pure. The dissolved solid and gaseous impurities in the water are frozen out and begin t o deposit on the face of t h e ice; but the currents of water set up by air agitation wash these impurities off t h e surface of the ice and carry them towards the center of the can. The impurities in the raw water thus become concentrated in the unfrozen water in the middle of t h e can. If these impurities are insoluble, their accumulation in this unfrozen water usually becomes so heavy t h a t eventually t h e currents of water set u p by the air agitation are not powerful enough t o keep the particles in suspension. As a result, these white or colored particles begin t o deposit in the ice before t h e cake is frozen solid, or, if the impurities are soluble, such as sodium salts, their concentration may become so great t h a t freezing is materially retarded. I n either case this concentrated impure water, or “core water,” as i t is termed, is generally removed, usually with a suction pump, and replaced with fresh water. The solids and gases left in the core water, or introduced in the fresh water replacing it; appear as white 1 Presented before the Division of Water, Sewage, and Sanitation ah the 60th Meeting of the American Chemical Society, Chicago, Ill., September 6 to 10, 1920.
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or colored deposits, and as air needles in the core of the ice when the cake is frozen solid. OBJECTIONABLE IMPURITIES
The most objectionable impurities in raw water for ice making are the compounds of magnesium, calcium and iron, organic matter, silica and alumina, a n d sodium salts. A word about each will be in order. CALCIUM A N D M A G N E S I U M c o w o u m s - T h e most common, and a t t h e same time most undesirable class of calcium and magnesium compounds are those causing temporary hardness-that is, the bicarbonates. Just as heating a water of this nature causes precipitation of the normal carbonates, so will freezing i t drive off the loosely held “half-bound” carbon dioxide a n d cause a precipitation in the ice of the normal carbonates, and possibly of magnesium hydrate. With air agitation, these precipitated compounds will be carried more or less completely t o t h e center of t h e can. Here they will accumulate until i t becomes necessary t o pump out the heavily laden water and replace i t with fresh water. Frequently this accumulation takes place so rapidly t h a t two, and sometimes even three, core pumpings are required. Even with good air agitation, however, the removal of the precipitated compounds t o the middle of the can is often not complete, and milky white /dots, bubbles, and patches are found distributed throughout the clear portion of the ice. Frequently, also, a white opaque shell of the precipitated carbonates will be found around t h e lower portion of the cake, where freezing is most rapid. When ice containing t h e precipitated carbonates melts, it leaves this objectionable sediment. Softening with lime removes the bicarbonates effectively and cheaply, and leaves in the treated water no products of the reaction beyond the 2.5 t o 4 grains per gallon of calcium carbonate and magnesium hydrate generally considered the limit of the lime reaction in the coId. The removal of permanent hardness is far less important for ice making t h a n temporary hardness. Investigations now under way indicate t h a t in a great many cases, possibly all, permanent hardness need not be removed, provided t h a t the magnesium, which always tends t o make white ice, is removed from such compounds and replaced with calcium. This is accomplished, of course, in the treatment with lime. The calcium sulfate and chloride left in the water as a result of the lime treatment appear t o be no more detrimental, and in some cases even less so, than the sodium salts which would result from the removal of the permanent hardness with Soda ash. I n a number of cases with waters of widely varying nature, we have discontinued the use of soda ash. I n practically every instance, ice made with the plain lime treatment is equally good or better than when soda is used. I n addition, sedimentation in the softening tanks is more complete, reducing the load on the filters. Further, when no soda is employed, the carbonate ions in the treated water are lessened, and. as the ice freezes, a much greater concentration in the unfrozen water is required before the ion-product constant is exceeded.
Vol. 13, No. 3
As a result, the unfrozen water remains clear much longer, free from particles of the precipitated carbonate t h a t would tend t o deposit in the ice; consequently, core pumping can be delayed, lessening the amount of water and refrigeration thus wasted. IROK, SILICA, A L U M I N A , A N D ORGANIC MATTER-AS little as 0.2 p . p. m. of iron ma cause “red ice”-tbat is, ice colored red-brown, chie y in the core. Silica and alumina are deposited in the core of the ice cake, imparting a muddy appearance t o i t ; when this ice melts, a gray, slimy sediment remains. Organic matter is frequently found in objectionable quantity in surface waters, particularly in warm weather. It usually colors the core of the ice a muddy or bright yellow, which is sometimes so objectionable t h a t the ice is difficultly salable, even though otherwise of good quality. Lime-soda softening of the raw water, followed by sand filtration aided by t h e use of a coagulant, effectively removes t h e iron, reduces t h e silica and alumina usually b y a half t o three-fourths, and greatly lessens the amount of objectionable organic matter. I n removing organic matter, we have in some cases found helpful t h e use of bleaching powder, applied with the softening chemicals. SODIUM sALTs-The chief objection t o sodium (and, of course, potassium) salts is t h a t they accumulate in the core water, retarding freezing. and are finally deposited as white solids in the ice. If considerable sodium salts are present, t h e lengthening of t h e freezing period may be so serious t h a t several core pumpings and fillings with fresh water may be necessary. I n addition t o this general objection, certain sodium compounds have specific undesirable effects. Sodium bicarbonate in considerable amount tends t o cause brittleness and cracking. Large quantities of sodium sulfate tend towards the formation of a white shell on the outside of the ice, giving the entire cake a n opaque appearance, even though the interior portion is quite clear. Treatment with lime converts the bicarbonate of soda t o the normal carbonate and decreases somewhat the tendency towards brittleness. Softening has no other beneficial effect on sodium salts. T h e only practical way t o remove them, of course, is by distillation.
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CORE P U M P I N G
Core pumping involves a number of very serious losses, There is the expense of refrigerating the fresh water, the d‘ecreased plant capacity due t o the extra time necessary for freezing this fresh water through the excellent insulation of the surrounding ice, the labor required, and the cost of pumping, and of the water itself, These combined losses are so heavy t h a t , in many cases, if competition for trade is not keen, the ice maker will not pump cores when they really should be pumped, and will produce a cake of ice having a heavy white or discolored center, instead of a thin, colorless, tasteless, and practically transparent one. From the standpoint of core pumping, t h e most objectionable impurities in raw water are those causing
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temporary hardness, due t o the heavy, gritty sediment formed by freezing out the half-bound carbon dioxide. When, as is frequently the case, the impurities in a raw water are chiefly of this nature, softening with lime reduces the offending substances so much t h a t i t is often possible t o produce first quality ice without core pumping, provided the air agitation is not stopped too soon. Even when the presence of large amounts of impurities other than temporary hardness, or when improper air agitation prevents entire elimination of core pumping, lime-soda softening reduces t h e quantity of water t h a t must be pumped. Usually one small core pumping is all t h a t is required. This effects a very material saving in water and refrigeration, and, in a large plant, of labor. The freezing time is also shortened, increasing the plant’s output. CHECKING A X D CRACKING
A4very unwelcome and expensive phenomenon in an ice plant is the tendency of the ice t o crack and shatter, particularly when low brine temperatures are employed. There has been no satisfactory explanation advanced for this tendency, beyond t h a t the ice is evidently frozen under an internal strain. I t would appear t o be quite possible t h a t the presence of bicarbonates in the water is chiefly responsible for this strain. During the freezing process, while the half-bound carbon dioxide is trying t o escape, the ice continues t o crystallize, entrapping bubbles of gas and particles of the precipitated compounds, which are readily visible. The ice thus formed is comparable t o a metal casting full of blowholes and impurities, and is in consequence inherently weak and brittle. Some weight is given this hypothesis by the general experience t h a t removing the bicarbonates of calcium and magnesium from a water by treatment with lime results in t h e production of much clearer and firmer ice, and frequently permits the use of lower brine temperatures. Further, in a recent series of experiments, ice was frozen from water t o which had been added varying amounts of sodium bicarbonate. I n all cases except the lowest concentration (10 grains per gal.) the ice formed was quite brittle, cracked readily, and showed considerable evidence of a bubbly structure. Analysis of the melted core ice showed the conversion of the bicarbonate t o the normal carbonate in all cases t o the extent t h a t the normal carbonate alkalinity averaged 35 per cent of the bicarbonate alkalinity. ZEOLITE S O F T E N I N G
It is this relation of bicarbonate alkalinity t o brittle and bubbly ice which is probably partially responsible for the unsuccessful application of zeolite softening to the manufacture of raw water ice. Contrasted with the actual removal of the bicarbonates of calcium and magnesium t h a t is effected by softening with lime, the zeolite or base exchange process leaves in the treated water the slightly greater equivalent weight of sodium bicarbonate. Calcium and magnesium sulf a t e are converted t o sodium sulfate, which has the disadvantages already discussed. Iron, silica, alumina,
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and organic matter are not eliminated or reduced b y zeolite softening. LIMITING SALT CONCENTRATIONS
Finally, the question arises as t o t h e limiting quantities of the various impurities t h a t a raw water can carry and still make first-quality ice. We do not know exactly as yet, in all instances. Obviously, in the cases of the bicarbonates of calcium, magnesium, and iron, the limiting concentrations are their own solubilities, since softening with lime leaves the same residual content regardless of the initial concentration. I t is also probable t h a t the permissible maximum of silica and alumina is not exceeded in natural waters, if treatment with lime is employed. With regard t o sodium salts, and to calcium sulfate and chloride, investigations are now under way as t o the limiting concentrations possible, and the results will be published when completed. Tentatively, i t would appear t h a t when the total soluble salt content of a raw water exceeds 30 t o 40 grains per gal., exclusive of the temporary hardness, first-quality raw water ice cannot be made even with softening and highpressure air agitation. NOTE ON PARTIAL AND TOTAL IMMERSION
THERMOMETERS’ By C. W. Waidner andE.F. Mueller BURSAVOF STANDARDS, DSPARTMENT OF COMMERCE,
WASHINOTON, D . C. Received December 13, 1920
To avoid the necessity of applying the correction for the emergent stem, so-called partial immersion thermometers are made, which are pointed and calibrated t o reacl, as nearly as possible, correct temperatures when immersed t o a definite mark on the scale, e . g., 8 cm. above the bottom of the bulb. The indications of such thermometers are obviously influenced t o some extent by the temperature distribution above the bath; for example, if the thermometer were used in a bath, the top of which was insulated, the indications would be somewhat different from those obtained in a n open bath where the emergent stem would be heated by convection currents. The difference would be still more marked if the thermometer were used in a small bath heated by a gas flame. Such thermometers should be marked ‘(. . . . cm. immersion” or its equivalent, and should be provided with a mark on the stem t o indicate the depth of immersion. The reliability of the corrections certified as applicable t o partial immersion thermometers is necessarily somewhat less than t h a t of the corrections certified for total immersion thermometers, but this does not by any means imply that, if both thermometers are used with partial immersion, more accurate results will necessarily be obtained with the total immersion thermometer. R E L A T I V E ACCURACY OF P A R T I A L A N D TOTAL I M M E R SI 0 N T H E R M 0 MET E R S
For general laboratory use the partial immersion thermometer has some very evident advantages. I n 1
Published by permission of the Director of the Bureau of Standards
