Julv. 1924
I-q’D USTRIAL A N D ESGINEERING CHEAVIXTRY
719
T h e Case-Hardening of Steel by Boron and Nitrogen’ By T. P. Campbell and Henry Fay MASSACHUSETTS INSTITUTE O F TECHXOLOGY, CAMBRIDGE,
MASS
the boron is not wholly comK VlElV of the recent The case-hardening effects of boron and nitrogen on a low-carbon bined in the form of borides work in this laboratory steel haoe been studied experimentally. of iron, but part of it is left on the role played by Boron penetrates the steel in much the same manner as does carbon in the form of a hard solution. He also predicts that, nitrogen in the case-hardenunder similar conditions, but the boron-hardened steels show “whereas annealing is reing of stcel by carbonaceous marked difference in their response to heat treatment and are n e w so quired to produce the necessubstances,2 it was thought hard as steels containing an equioalent amount of carbon. sary hardness on articles casethat an investigation of the Nitrogen is much more readily absorbed by a boron steel than by a hardened by carbon, boron case-hardening action of should confer this hardness carbon steel, this increase in absorptive power being due to the without any heat-treatment .’ ’ some other closely allied formation of boric nitride at temperatures abooe that at which iron The iron used in his inelement would be of interest. and nitrogen unite to form a stable nitride. Boron steels thus vestigation had the following The purpose of case-harden nitrified show those properties which would be expected in a steel of composition: ing is, primarily, to produce high nitrogen content-oit., extreme brittleness and a marked Per cent a very hard, wear-resisting tendency toward exfoliation, chipping, etc. c , . . . .. . . . , , 0 . 1 2 0 case around a soft, tough Analytical data, hardness numbers, and photomicrographs are Si . . . . . . . 0.020 M n . . . . . . . . . 0.160 interior. I n practice this is given in substantiation of the conclusions drawn. P . . . .. . . . , . . 0.060 usually accomplished by S . . . . . . . . . . . 0.040 heating: the object in some suitable medium, the temperature and duration of heating de- The specimens were made in the form of cubes, holes being drilled in the center to about half their depth. As a case-hardenpending upon the medium employed and the desired proper- ing powder, “pure amorphous boron” and a fine powder of 19 ties of thcobject after the hardening. Steels thus case-hardened per cent ferroboron were taken. One or the other of these must be double heat-treated subsequently, in order to remove substances was placed in the drill-hole of a specimen, and the hole was then closed with an iron stopper under a hydraulic press, strains and to refine the graiv of the case and of the core. The specimens thus prepared were heated in a silica tube in a The present investigation was conducted with a view to Heraeus furnace. The thermocouple of a LeChatelier pyrometer finding what effects could be produced by case-hardening with was placed close to the tube. In order to eliminate the influence boron instead of with carbon, also what effect nitrogen of a gaseous medium, the air was removed from the tube by means would have on a steel thus treated. I n other words, what of a mercury pump. The heating was of 2 hours’ duration a t 950” C. Under these conditions the boron “penetrated the iroq would be the physical and chemical properties of iron-boron to a depth of 1 mm.” and iron-boron-nitrogen alloys as produced under conditions As the result of this investigation, Tschischewski concludes that : approximat’ingthose obtaining in practice? (a) Cementation procedes more easily and quickly with ferro?
I
,,,
PREVIOUS WORK The only work discovered bearing directly on this problem was done by Tschi~chewski.~The first part of his work consisted of a study of the system iron-boron. He determined the cooling curves arid established the equilibrium diagram of the system up to about 12 per cent boron. For this purpose Swedish nail iron was melted in a porcelain tube in a Tamman furnace; the boron was added to this in the form of finely divided ferroboron of about 24 per cent boron content. The charge in each case was 100 grams. During the heating (1500” to 1550° C.) the alloy was stirred with a silica rod, and the time of cooling to 650” C. was 30 1.0 35 minut.es. Microscopic examination of the specimens thus obtained showed that: ( a ) A pearlitic constituent occurs a t as low as 0.08 per cent boron. ( b ) A eutectic occurs a t 3.11 per cent boron. The ferrite portion of this eutectic is a solid solution of Fe2B in iron. (c) Above this point free iron boride occurs in well-defined crystals; a t about 8 per cent the boride is held very loosely and a t 8.5 per cent the alloy crumbles in the fingers. Above 9 per cent the alloy shows a differentiated structure with better mechanical properties. Microphotographs are given showing the change in structure with increasing boron content. The results of the cooling curves are shown in the equilibrium diagram (Fig. 1). A portion of the iron-carbon diagram is shown in dotted lines to bring out the close resemblance of the two systems. The second of Tschischewski’s papers is entitled, “The CaseHardening of Iron by Boron.” He says that this investigation was prompted by a consideration of the fact that, as shown by the equilibrium diagram, on cooling the alloys of iron and boron, ____.
Received February 13, 1924. Fay, Chem. Met. Eng., 24, 289 (1921); Sawyer, A m . Inst. Min. Met. Eng., 69, 798 (1923). 8 I r o n A g e , 98, 396 (1916); J . I v o n Steel. I n s t . (London), 92, 614 (1915); 96, 185 (1017). 1 2
,
boron than with pure amorphous boron. ( b ) Microscopical examination shows that the hard, white layer of the case-hardened portion consists of compact “boric pearlite” with a twin-crystal structure (etched with hot sodium picrate solution). The edges of this layer contain a subeutectic alloy of ferrite-pearlite; the ferrite in this instance contains the boron in solid solution. (c) Case-hardening a t a lower temperature than the above yields an alloy containing less boron. This alloy is not so hard and brittle as that already described. He gives no hardness determinations, no data on the penetration of the boron with time or with temperature, nor does he say anything about the effects of quenching or other heat treatment. In a recent paper of the Bureau of Standards entitled “The Manufacture and Properties of Steel Plates Containing Zirconium and Other element^,^ some interesting information is given on the mechanical and physical properties of boron steels. The results of the various tests given are hardly comparable with those of Tschischewski because of the presence of other elements which are known to have pronounced effects on the properties of steels-e. g., nickel, silicon, manganese, etc. The following are the results of a series of inverse rate cooling curves on the steels shown: ---Percentage----C Si Mn Ni B 0.38 1.00 0.75 2.90 0.30 0.16 1.30 0.64 2.80 0.49 0.45 0.33 0.69 0.06
..
--Temperature C.-7 Acl Acz-a Ars-2 Ari 741 782 640 588 745 817 685 590 760 785 714 675
Ingots containing up to 0.73 per cent boron were heated to 1100”C. for rolling. These ingots fell apart upon removal from the furnace under their own overhanging weight, “furnishing a striking example of hot-shortness.” A few ingots containing only 0.23 to 0.46 per cent boron were partially rolled, but broke u p under the rolls and, in fact, “were so .hard to roll that two of the coupling collars of the mill were also broken a t the same time.” 4
Bur Standards, Tech. Paper 207 (1922).
INDUSTRIAL A N D ENGINEERING CHEMISTRY
720
After special heating of two ingots, plates were rolled, but these plates showed numerous cracks and fissures. These results are certainly not very encouraging for the future of boron steels. However, Guillets states that boron steel per se is of little use unless tempered, when it has a “high tensile strength and elastic limit, and great resistance to shock.” Such a steel would contain about 0.22 per cent carbon and 0.5 p a cent boron, the latter having been added, as ferroboron, in the ladle. I
Percenf Boron FIG.I-IRON-BORON DIAGRAM (TSCHISCIIEWSKI) Dotted line, iron-carbon equilibrium diagram
EXPERIMENTAL For studying the penetration of boron, low-carbon steel specimens were heated a t various temperatures in finely divided ferroboron for different lengths of time. These specimens were in the form of bars about 15 cm. (6 inches) long cut from a long rod of approximately 2.5 cm. (1 inch) diameter. This steel had the following composition: Per cent 0.12
c .......
... .......
Mn.. P
0.38 0.033
Per cent
S... . . . . 0.034 N ....... 0.0003
Si..
.....
Trace
Vol. 16, No. 7
the method of Hurum and Fay.’ This method admits of a high degree of accuracy, and is especially well adapted for determinations of small amounts of nitride nitrogen. The matter of a suitable boron analysis, however, was not so easily settled. The best form of analysis found was that of Wherry, as applied by Lindgren.8 This method consists essentially in dissolving the steel sample in aqua regia, diluting, and precipitating the iron with calcium carbonate. After filtration and washing, the filtrate is titrated with 0.1 N potassium hydroxide solution, using phenolphthalein as indicator. This method has several disadvantages: first, all the solutions used must be quite free of carbon dioxide, since carbon dioxide is stronger than boric acid; second, the alkali borate formed as the result of the titration hydrolyzes readily, thus throwing off the end point. To correct for this, mannite is added in 1-gram lots until a further addition produces no color change. When working with very dilute solutions, however, it is almost impossible t o hit the end point; in fact, the accuracy of the entire analysis, for boron concentrations (in the steel sample) of 0.10 per cent or less, is scarcely better than 10 per cent and decreases with decreasing boron content. A consideration of this problem led to the development of the following electrometric method: The solution resulting from the precipitation and filtration of the iron is placed in a small (200-cc.) beaker. A Clark hydrogen electrode is then introduced, and as soon as the hydrogen flow has become steady, the tip of a tube leading to a standard calomel element is placed as near the hydrogen electrodeaspossible. This tube contains a saturated solution of potassium chloride, as does also the calomel element, and the tip is loosely plugged with cotton to minimize diffusion. There is thus formed a voltaic cell, the e. m. f. of which depends solely upon the concentration of hydrogen ions in the boric solution. I n the present investigation this e. m. f. was measured by means of a potentiometer using a wall galvanometer of about 5000 ohms resistance. The boric acid concentration corresponding to a given value of E may be computed from the relations: E = 0.2495 0.0591 log H f
+
The ferroborone had the following composition: Per cent
Si
4.32
Cr
.... .....
Fe.. Al.
78.79
Per cent 2.03
....... C .......
B ....... 14.14
......
0.07 0.70
The heating was carried out in an alundum tube resistance furnace. The specimens were placed in a cast-iron cylinder; the ferroboron was then packed in around the specimen, and the end of the cylinder closed with a tight screw cap. The hot junction of a platinum-rhodium thermocouple was inserted next to the cylinder in the furnace, the cold junction being maintained a t room temperature, and the resulting potential was read from a millivoltmeter. The corresponding temperature differences were obtained with an accuracy of about 5 ” C. from a calibration chart. This arrangement was found so satisfactory that it was used for all the runs in which ferroboron was the cementing medium. For heating in ammonia the same furnace was used, the ends of the alundum tube being stoppered in such a way that ammonia gas from a tank could be passed over the specimen, the latter being supported on two quartz brackets so as to obtain even exposure to the action of the gas. It soon developed from the preliminary runs that accurate chemical analyses for nitrogen and boron would be of interest in showing quantitatively the relative and separate rates of penetration of these substances into the steel under varying conditions. The analysis for nitrogen was made according to fi 6
“Gtude Industrielle des Alliages Mdtalliques.” Furnished b y the Union Carbide Company.
where K is the equilibrium constant for the primary dispociation of the orthoboric acid, and has the mean value 6.61 x a t 25” C . The term H3B03 in the denominator of Equation 2 represents the equilibrium concentration of boric acid; but this may be taken as giving the total concentration with an error of less than 0.05 per cent when this conequivalents per liter. The centration is less than equivalents per liter of boric acid being known, the weight of boron may be computed a t once from the fact that Equivalent H3B03X 11 = grams B
The general scheme of connections for this electrometric determination is given in Fig. 2. Here P is the cotton plug and C is the calomel element; the rest of the diagram is self-explanatory. A few precautions must be observed in using this method. First, all solutions must be free of carbon dioxide. Second, inasmuch as the resistance of the boric solution is extremely high, being of the same order as that of good distilled water, every means must be employed to minimize the effect of this resistance. The actual ohmic resistance of this part of the circuit varies directly as the length of the path; hence the tip P of the tube connecting with the calomel element should be placed as close as possible to the electrode. Further, since the presence of a n y other ions of greater mobility than those of the boric acid has a marked effect on the e. m. f., the 7 8
Chem. M e t . E n g . , 26, 218 (1922). J. A m Chem. Soc., 3 0 , 1687 (1909).
INDUS'TRIAL A N D ENGINEERTh'G CHEMISTRY
July, 1924
tube from the calomel element should not be introduced until everything is ready-i. e., until a setting for null-point can be obtained in the shortest possible time-otherwise, diffusion of chloride and potassium ions will throw the determination out entirely. The presence of gases other than hydrogen in the platinum electrode is especially to be guarded against. Atmospheric oxygen is the most common of these; it may be removed by making the electrode the cathode in a n electrolysis cell, in which case the oxygen is reduced to water. When the electrode is not in use it should be kept in a stoppered jar of distilled water. With all precautions duly observed, the ultimate accuracy of setting of the potentiometer was found to be =&0.00005volt. The resulting accuracy in boron percentage is, however, well within the limit of experimental error of the rest of the analytical work, and certainly is sufficient for the purposes of this investigation. Following the first determinations of boron and nitrogen, it was thought that the action of elementary boron might produce higher surface concentrations of boric alloy than had hitherto been obtained. After several attempts to obtain the element by thermal reduction with magnesium and aluminium, it was found that the method devised by Weintraubg yields a very pure form of fused metallic boron. An intimate mixture of pure charcoal and fused boric oxide was heated in a quartz tube through which bromine vapor was passed. The resulting boric bromide was collected in a trap, while the excess bromine was passed through a condenser and collected in the liquid form. The boron bromide was then placed in a distilling flask, the exit tube from which led into a Pyrex tube in which was established a high-tension, A. C. arc supplied by a 110-11,000-volt, 300-watt transformer. The entrance tube was placed tangential to the wall of the Pyrex tube and below the level of the lower electrode, so that the ascending column of vapor was given a spiral motion along the arc flame, much as in the Schoenherr process for nitrogen fixation. The distilling flask was then gently heated until the liquid boron bromide boiled fairly energetically (95 O to 96 O C.). The vapor thus forced up through the tube was decomposed by the arc, yielding granules of fused boron and bromine vapor. Needless to say, this method is very cumbersome and tedious, but it does yield a very pure form of boron. The small amount of boron thus prepared was used in the manner described by Tschischewski, and yielded a case high in boron; but the form in which the experiment must be carried out precludes the possibility of any hardness determi9
Trans. Am. Electvochem. S o c , 16, 165 (1909).
72 1
nations, and the method of preparation of the boron precludes any extensive investigation along this line. In an attempt t o get some other medium high in boron and containing a minimum of foreign substances, which would complicate the interpretation of results, a variation of the Goldschmidt process was found very satisfactory for producing pure ferroboron of high boron content. 04
I
2 Hoursin FerLoborin a i
--
SOO'C I Hour in NH3 at S O O Y
I
I
I
4 Hours in Ferroboron at 9oo°C.
0.3
s-$
$4
0.2
7.
+-s 5b
4? %h 0.1 7
Q D
0.01
FlG.
0.02 0.03 0.04
%-ANALYSTS
0.m 0.01 0.02 0.03 0.04 aos 0.06 Pene frafion Inches
D,OZ
O F S T E E L FOR
BORON AND
0.07
hTITROCEN
The method used consists in making up a charge of powdered boric oxide, pure anhydrous ferric oxide, and powdered aluminium in the desired proportions. This charge is placed in a crucible of such size that the charge occupies about two-thirds of the volume. A booster charge of aluminium and sodium peroxide is placed on top of the main charge, and a magnesium ribbon is stuck into the top. The whole charge, except the ribbon, is then covered with a layer of fluorspar. Ignition is effected by burning the magnesium ribbon. For best results, it was found that the boric oxide should not exceed the amount required to make a 40 per cent ferroboron; it was also found that the reaction goes most readily when the crucible and charge have been given a thorough heating (almost to a dull red heat) before ignition. The ferroboron thus prepared contains no carbon; in fact, if due care is taken in the selection and preparation of the materials, the only impurity present is aluminium, and that in quantities not greater than those occurring in the commercial product. The results of the various runs using this ferroboron and other media are given below.
RESULTS From the work of Tschischewski it was evident that there would be little, if any, case-hardening effect a t temperatures below 800" C. The first experimental work, then, was designed to find how penetration and surface concentration would vary with duration of heating at any given temperatures, and to determine the variation of these factors with increasing temperature and constant time of exposure. Table I shows the results of the first runs:
H2
TABLEI
U
I
H E A T TREATMENT No. 1 1 hour in 14 per cent ferroboron at 800' C. Furnace cooled 2 1 hour in 14 per cent ferroboron at 860' C . Furnace cooled 3 1 hour in 14 per cent ferroboron at 900' C. Furnace cooled 4 3 hours in 14 ner cent ferroboron at 900' C. Furnace cdnled 5 4 hours in 14 per cent ferroboron at 900° C. Furnace cooled 6 1 hour in 32 per cent ferroboron at 900 O C . Furnace cooled
Shore Hardness 10
Brinell No.
82.5
10
82.5
10 t o 12
82.5
12 to 15
91
12to 15
91
12 to 15
91
An examination was made of the microstructure of each
I piece, and it was evident that for a given boron concentration FIG.. 2 - A P P A R A T U S
FOR E L E C T R O M E T R I C
ANALYSIS O F BORON
in the medium, the amount of boron absorbed was propor-
tional to the iluration of heating and tu the temperature. Analyses taken in conjonction with the microstractiirc, liowever, also show that,, although the amount absorbed may increase n.ith the t . k e of heating, the surface concentration attainable, using a given ferrobornri and a givcn tanperature, reaches a maximom after a certain time of expasure, subsequent. hentitig at the given temperature simply cause? deeper penetration, but no increase in surface concentration. The hariiness numbers nlso hriirg out this faet~. Tlte effect of iiitrogen on some of these specirtierrs was tliert studied. 4 . speeirnenws heated in 14 per cent ferrriboron fur 2 hours at 900" C., cooled in the furnace, polished, and reheated for 1 hour in ammonia at 900" C. Aftcr cooling in an rimmonia atmosphere in tlic furnace, tire specimen appeared silvery gray in color, and ltnd the following hardness qualit' Brinell, 101, The hardness nmiibers sliow that t.he nitride c a w is hrit,tlo rather than hard. This may r sei-ateiiiog a speeiriteit with a Rirs off in small chips.
An analysis of ariotlier such specinieir rlioiwd the fi~lliwing rewits : ( a ) Treelnzent. Heated for 2 hours at 900" C. in 14 per cent Icrroboron: cooled in furnace, and polished; reheatcd for 1 hour in ammonia at 900" C., and cooled in t h e furnace. Successive concentric layers of thickness shown were turned OR on a lathe, and analyzed for boron and nitrogen.
(6) Analyses: Thickness oi Layer cm. lrrelres n 03u5 0.012 0,0229 (1.009 0.l1229 0.009 ,1.038li 0.013 u.n6i18 (1.020
Boron Per cent II.080 0,261
0.263
Nitrogen Per cemt 11.633 U.Il23 lI.021
o.00a 0.0012
0.107
u.012
In contrast to tliis, the following is an analysis, made in the same way, of a spccimci~heatcd for 4 liours in ferroboron and c o i h l in the funisce: avron
Thirkeesr d h y e r C",. Inches 0.0270 0,1111 0.010 0.0254 lt.ll229 It.11l~9 0.010 0.254
Per cent 0 . m 0.486 IJ.li4 0.070
These result,sare pIot,t.cdi i i the ciirves sliown in Fig, 3, and, talien in conjunction with the above, bring out some vcry interesting facts. First., the hnmn penetration follows a riiirnial diffusion curm in the ahieiice of nitrogen. Second, wheu sircii a specimen is heated in arirmonia, the nitrogen displaces the boroii at t,he snrfacc---i. e., tlic boron concnntration reaches a niaximnm value at some distance in from the edge, aft,cr wliicli tlie tu-o concentratims fall off at about tlic same rate. Third, this sizrfsce nitride is fiirmed at, a temperature atwliich iron n i t r i d e i s onatable; a,nri, fixtiter, the ammmt of nitride resulting in t.lie surfare layer is more than would he formed if only iron and nitrogen w i n present. In proof of this statement,, the following experitneiit v a s performed: .A specimen ~vusheated for 4 liours in 11 per cent ferroboron n t 900' C., cooled in the fiirnace, and carefiilly polislied and weiglied. It was then rclieateil for s i s l i i ~ v mbelou;. After each heating the woighed, and upon being replaced in the furnace was given a different orientation SO as to equalize tire ahsorptiim. The results wen, as follows: 0 1 2 4 ti
10
22.4125 22,13681 22.88iX
22. 7031
22.705~1 22,7313
Tlirti t,he net gain in weight is appr~:xiimately0.3!1 per cent. 1 % ~way . of comparison, HurnnP Iieated a piece of soft iron wire in ammonia at 900" C., uiider a pressnre of 4 atmospheres for a period of 15 horrrs, and t,lie net gaiii in weight was oiily 0.123 per cent. Taking all these facis into ronsiileration, and remembering that tioroil has a marked affinityfornitmgen at elevated temperatures, it is reasonahlo to conclude that the abnormal absorption of nit,rogen sltowii by these speeimetis is acconnted For by the nitrogen "carrier" action of the boron. That is, a t tho ternperat.ures employed, homn has a greater affinity For nitrogen than has iron. The nitrogen is absorbcd, in ihe first instanre, in the fnrnr of boric nit,ride, which on slow to the iron, tlic boron being at rxiuling yields up its i~it.r(~geii t,he same time rejected toward t,lie interior of the specimen. That S O I ~ C boric nitride ii; formed nrrder the conditions outlined may he shown by queiieliiiig a specimen from a high tcmpcrature after it, has been heated in ammonia for some l,ime. \i'lien tiic red-hot specimen strikes t,lie water, 10
Thesis, Massachusetts lnriitufe 01 Technology, 1919.
INDUSTRIAL AND ENGINEERING CHEXISTRY
July, 1924
a noticeable odor of ammonia is given off, and upon removal from the bath the specimen may show a light coating of boric acid crystals, provided it is withdrawn from the bath almost a t once. Moreover, subsequent examination of the specimen under the microscope will show that scarcely any nitride is left, whereas the same specimen cooled in the furnace would show a high concentration of nitride needles a t the surface. I
I Ambunti of boroh Absorbed in lmm. Case af Different Temperatures
723
medium causes an increase in surface concentration of boric alloy. The hardness increases with the surface concentration, but never reaches any value comparable with the hardness of a steel surface containing an equal amount of carbon and treated in the same way. In fact, these results seem to bear out Guillet’s statement on boron steels-viz., that after heat treatment they show elasticity and resistance to shock, but no great degree of hardness. It will be noticed that the curves of absorption and temperature show a decided maximum, occurring between 1100” and 113.5” C. Boron steels show many similarities in the mechanism of their absorption and diffusion phenomena to carbon steels. This might, of course, be predicted from the relative positions of the two elements in the periodic table. The very close resemblance to the two systems is brought out by the similarity of the equilibrium diagrams shown above, and this similarity is confirmed by microscopic examination. ACKNOWLEDGMENT The authors wish to express their gratitude for generous aid received from the C . M. Warren Fund of the American Academy of Arts and Sciences.
The Use of Cool Solutions in the Jones Reductor”z By G. E. F. Lundell and H. B. Knowles
Temperafure “C.
BUREAU O F STANDARDS, WASHINGTON, D . C.
FIG. BOR BORON ABSORBEDIN ~ - M MCASE . AT DIFFERENT TEMPERATURES
.
A microscopic examination of the specimen that had been heated for 10 hours in ammonia showed a structure that bears out the conclusion already drawn as to the action of nitrogen on a boron steel. At the very edge the nitrogen had been abrorbed to the extent of about 10.5 per cent, as shown by the large amount of iron-nitrogen eutectoid occurring in this region. Below this was a region of decreasing nitrogen concentration, while still farther in was a comparatively small band of boric pearlite. Fig. 4 shows a composite appearance of a cross section of this specimen. The large, black areas a t the top are the iron-nitrogen eutectoid; the lower portion shows clearly the decreasing needle concentration and the boron-iron eutectoid region. Up to this point the investigation had been concerned with the manner of penetration and chemical properties of the alloys formed more than with the physical properties of the specimens. A series of runs was then made, the object of which was to produce a maximum surface concentration of boron-iron alloy, and to find the relation between this concentration and hardness. Table I1 (see also curves in Fig. 5 ) shows the results of these runr. Boron in Ferroboron Per cent 14
32
Fmp. C. 8 50
9 00
1000 1100 1160 900 1000 1100 1150
TABLE I1 Time of heating, 4 hours Boron in 1-Mm. Case Shore Per cent Hardness 0.27 12 0.53 15 17 1.08 2.96 25 22 1.32 19 0.88 1.7s 24 32 3.02 2.92 28
Brinell No. 82.5 91.0 110 162
150
110 155 20 1 183
All the foregoing specimens were quenched from above 900” C. These figures bring out very clearly the fact that increase in temperature or increase in boron content of the hardening
NE of the chief drawbacks to the wider adoption of the Jones reductor3 has been the belief, fostered by most texts, that reductions must be performed in hot or boiling solutions. The specification of such solutions has undoubtedly discouraged many who would otherwise have employed the reductor, while the faithful observance of these directions has caused much expense and inconvenience. This will be apparent when one considers that three different solutions must be kept hot or boiling, that large quantities of two of these must be constantly available when much work is done, and that the handling of boiling hot water or acid (oftentimes in a hurry) is not pleasant. The use of cool solutions for certain reductions is occasionally mentioned in the literature-for example, by Holladay4 and Johnson.6 A few texts specify hot solutions6 for one reduction and cool solutions for another.’ The experience of the authors goes to show that quantitative reductions result a t room temperatures (15” to 27” C.) and the usual speeds (2 to 4 minutes) in all present applications of the Jones reductor. As the use of cool solutions is so desirable, particu-
0
Received March 19, 1924. Published hy permission of the Director, U. S. Bureau of Standards. 9 For details concerning t h e construction of this desirable aid in volumetric reduction-oxidation analyses, consult Scott, “Standard Methods of Chemical Analysis,” Vol. I, 3d e d . , p. 320, D. Van Nostrand Co.; Blair, “ T h e Chemical Analysis of Iron,” 8 t h ed., p. 88, J. B. Lippincott & Co.; Treadwell-Hall, “Analytical Chemistry,” Vol. 11, 5th ed., p. 637, John Wiley & Sons, Inc. 4 “Notes on Reductor Technique” (as applied t o molybdenum), Scott, “Standard Methods of Chemical Analysis,” Vol. I, 3d ed., p. 320, D. Van Nostrand Co. 5 “Determination of Uranium in Steel,” Johnson, “Chemical Analysis of Special Steels, e t ? . , ” 3d ed., p. 365, J. Wiley & Sons, Inc. 6 Mellor, “A Treatise on Quantitative Inorganic Analysis,” p. 415, Chas. Griffin & Co.; Schoeller and Powell, “The Analysis of Minerals and Ores of t h e Rarer Elements,” pp, 120, 165, a n d 187, Chas. Griffin & Co.; Scott, loc. cit., p. 370. 7 Mellor, loc. cit., p. 190; Schoeller and Powell, loc. cit., p. 3; Scott, Zoc. a t . , pp. 320 and 356. 1 2
