Mar.,
1920
T H E J O U R N A L O F I N D U S T R I A L AiVD E N G I N E E R I N G C H E M I S T R Y
A t present there prevails a rather uncertain conception of the significance of the term “cellulose” as applied t o material derived from woods. I n general, i t may be understood t o mean a product prepared by processes of sufficient intensity t o remove all extractives (resins, dyes, etc.), incrusting substances (lignin), and hemicelluloses (condensed carbohydrates of pentose, mannose, and galactose basis) and limited in their action t o those bodies. The chlorination process as applied t o wood material, treated with non-hydrolyzing solvents only, fulfills these requirements. The definition of cellulose as a residue remaining after alternating treatments with chlorine and sodium sulfite solution may be accepted if we add the limitation t h a t t h e process be preceded with non-hydrolyzing treatments only. The residue so obtained should be free of lignin and hemicellulose, including pentosans, mannans, and galactans. I t may contain CY-, p - , and y-cellulcses corresponding t o t h e definitions of these bodies implied by the conditions of t h e mercerization test, also furfuralyielding complexes, b u t should be free from easily hydrolyzable pentosans. SUMMARY
I-A comparison is made of three proposed methods of treating woods and other lignified materials previous t o chlorination in the cellulose determination. These methods consist of ( I ) absence of hydrolysis, ( 2 ) alkaline hydrolysis, and (3) acid hydrolysis, restricted in each case t o the degree of intensity considered necessary for avoiding attack upon the cellulose proper. 11-The d a t a show t h a t all processes involving preliminary hydrolysis result in diminished yield of acellulose as well as total cellulose, and are therefore unacceptable as accurate cellulose processes. 111-The ratios of a-cellulose t o total cellulose are practically the same whether or not preliminary hydrolysis is used. This shows t h a t the highest type of cellulose is as strongly attacked during hydrolysis as the lower types. IV---During the treatments incidental t o chlorination the hemicelluloses are hydrolyzed and dissolved in t h e filtrates and washings. Preliminary treatment with the object of removing the hemicelluloses is therefore superfluous. V-A considerable proportion of t h e furfural-yiel ding complex (probably oxycellulose) remains in t h e residue practically unaffected by any of the hydrolytic treatments employed. The rest of the furfuralyielding material (probably xylan) is readily hydrolyzed and dissolved during chlorination. VI--The significance of t h e term “cellulose” as applied t o wood products is discussed. A RAPID ACCURATE METHOD FOR THE ANALYSIS OF AN IRON ORE By Ernest Little and Willard L. Hult RUTGERSCOLLEGE, NEWBRUNSWICK, N. J. Received September 22, 1919
The relative merits of the dichromate and permanganate methods for the analysis of an iron ore are too well known t o warrant any lengthy discussion of
269
them here. It is advisable, however, t o recall those particular points which have a special bearing on this article. ARGUMEXTS
FOR
AND
AGAINST
PERMANGANATE
AS
A
STANDARD OXIDIZING AGENT
The permanganate method is generalty used to-day, due t o the fact t h a t permanganate acts as its own indicator and gives a n easily obtainable end-point. Many possible errors, however, must be guarded against. The instability of the reagent makes necessary quite frequent restandardization. The solution should be kept in colored bottles and out of the light as much as possible. The introduction of organic matter, even dust, causes a reduction t o manganese dioxide. Treadwell, after giving data showing t h a t , the permanency of potassium permanganate is greatly increased by heating the solution, or allowing i t to age for z wks., and then filtering through asbestos, concludes by saying,‘ “For very accurate work, however, i t is advisable to restandardize the solution frequently.” Another troublesome feature is the reducing action of the chloride ion on the permanganate ion, necessitating the use of the rather unsatisfactory preventive solution with its possibly useless components.2 Fuming sulfuric acid may, of course, be substituted, but this operation, even in the hands of an experienced analyst, is liable t o introduce a percentage of error which is almost prohibitive in quantitative work. DISCUSSION
OF T H E U S E O F POTASSIUM DICHROMATE
AS A STANDARD OXIDIZING AGENT
The dichromate solution, on the other hand, is a permanent standard, little affected by traces of organic matter. The dichromate ion is, moreover, not reduced by t h e chloride ion, thus making the use of preventive solution, or its unsatisfactory substitutes, unnecessary. The necessity of using ferricyanide as a n outside indicator with dichromate, however, causes most analysts t o prefer the permanganate titration. Speaking of the use of dichromate as a standard oxidizing agent, Foulk says:3 “A solution of potassium dichromate, through a strong oxidizing agent, is perfectly stable under ordinary laboratory conditions. I t is unaffected by light, is not acted upon rapidly by organic matter, and does not act on dilute hydrochloric acid. The salt (KzCrz07) is easily obtained pure, and, if recrystallized and dried, is one of the best standard substances t o be used in determining the exact strength of oxidizing and reducing solutions.” He adds further: “The chief objection t o be made t o standard solutions of potassium dichromate is the fact t h a t no convenient indicator has yet been found for it.” The writers realized, therefore, t h a t if the dichromate method could be used with an accurate indicator in t h e solution, i t would be by f a r the preferable method. Little and Fenner have shown in their “Modified Dichromate Method for the Analysis of G I y ~ e r i n , ” ~ 1
Treadwell and Hall, “Analytical Chemistry,” p. 561. C h e w SOC.,32 (1910), 539. “Quantitative Analysis,” p. 167. J . A m , Lealher Chem. Assoc., June 1917.
* Hough, J . Am. 3
4
2
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
70
t h a t after oxidizing glycerin with a measured amount of potassium dichromate, the excess of dichromate can be determined by adding potassium iodide and titrating with thiosulfate, using starch as an indicator. I n this way the use of an outside indicator as directed i n t h e Official Dichromate Method’ for glycerin analysis was eliminated. T H E O R E T I C A L DISCUSSION
It will be seen a t once that the same scheme could be used in a ferrous iron titration were i t not for the presence of the ferric ion in solution, which is reduced by the iodide ion and iodine liberated. The question then is how this interference of the ferric ion can be eliminated. To answer this question, let us study the reversible oxidation and reduction reacJ 21zFe++ 12,and consider i t tion 2Fe+++ in terms of the two separate reactions: (A) zFe+++ zFe++ (3) (B) 21+(.I J Iz T h e tendency of Equation A in acid solution for ordinary concentrations is in the direction of the formation of ferrous ions. Like all similar reactions, however, equilibrium can be established by a proper adjustment of the two concentrations, and Peters has furnished data2 which show t h a t the reaction is in equilibrium when the following relative concentrations exist: C Fe++ lol’ a t 2 j 0 C. c-Fe+ff
+
-
+
+
-
+
Similarly, the action in Equation B is, for ordinary concentrations, in the direction of the formation of iodide ion, and Kuster and Crotogino have shown3 that a t equilibrium the relative concentrations of the two components are approximately as follows:
- 5.6 X -
1oZ9a t 2 j 0 c. CI2 Making use of these two constants and applying them to the reversible equation 2Fe++ Iz 2Fef++ 21we have a t e q ~ i l i b r i u m , ~ (CFe+++)2 X (CI-)2 5.6 X 1oZ9 = K = = 5.6 X IO-^. (CFe+f)2 X C12 (10’~)~ This equation is derived as follows: The quantitative expression of the oxidizing potential of Fe+++ is ~~~
+
+
~~
The potential of I ” as an oxidizing agent is RT E2 = log -__ ‘I2 X j . 6 X 1oZ9 2 (cI-)2 (assuming 5 . 6 X 1oZ9t o be correct). At equilibrium the two potentials will be equal, E1 = Ez RT CI RT (CFefff)2 X 1 0 = ~ ~ log X 5.6 X 1 0 2 9 2 log (CFe++)2 (cI-)z ~
~
3
THISJOURNAL, S (1911), 679. Z. phys. Chem., 26, 193. Z. anorg. Chem., 23, 88.
4
Stieglitz, “Theoretical Qualitative Analysis,” p. 274.
1 2
Vol.
12,
No.
(CFe+f+)2 X (CI-)2 - _ 5.6 X 1oZ9or 5.6 X IO-^. (CFef+)2 X C12 1 0 ~ ~
or
The constant of equilibrium is very small, hence t h e numerator of the above fraction must be small a n d the denominator relatively large. This is in accord with the well-known fact t h a t I- will reduce Fe++; t o Feff. I n view of the above expression of equilibrium, i t is evident t h a t the oxidation of the iodide ion could most easily be prevented by greatly reducing the concentration of the ferric ion. If this concentration is reduced t o a minimum, i t will necessitate a change in the concentrations of the other three components. These changes will, of course, be in the direction of reestablishing equilibrium, and since the concentration of ferric ions has been reduced, equilibrium could be brought about b y only increasing the concentration of iodide ions. The concentration of iodide ions is increased by having iodine oxidize ferrous ions t o ferric ions, the iodine being changed t o iodide. Thus we see t h a t by reducing the concentration of ferric ions the oxidizing potential for the equation Fe+++ Fe++ (%), which is represented by the quantitative expression C F e+++ E (volts) = R T log x 1017 C F e++ where R = gas constant and T = absolute temperature, is reduced below the oxidizing potential for the equation L I2 21b+), which is represented by the quantitative expression
+
+
--
and consequently we have not zFe+++ 2 1 - d zFe++ 12, but 2Feff Iz zFe+++ 21-. The interference on the part of the ferric ion is, therefore, eliminated.
+ +
-
+ +
APPLICATION O F THEORY
The simplest way t o keep the concentration of ferric ion low during the titration is by the addition of the fluoride ion, with which i t unites t o form a highly un-ionized ferric fluoride complex, probably FeFor. The efficiency of the fluoride ion in this connection is easily shown by putting a few cc. of N / I O ferric iron solution in a beaker. Dilute t o about 2 0 0 cc., add about 3 g. of ammonium fluoride and some potassium iodide. Not enough iodine is formed t o give even the slightest blue color with starch solution. The concentration of ferric ion has been reduced t o a minimum, and the results predicted in the above theoretical discussion have followed. Mott’ in his short iodide method for the analysis of a copper ore successfully eliminates Fe+++ from solution by changing i t t o the un-ionized ferric fluoride complex. Therefore, if during the analysis of a n iron ore by the dichromate method about 5 cc. in excess of diI
T h e Chemist A n a l y s t , July 1912.
Mar., 1920
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY
chromate are added, ammonium fluoride and potassium iodide introduced into the solution, and the iodine taken up by a “hypo” titration, using starch as an indicator, we have a method which possesses all the advantages of the regular dichromate method without the disadvantage of a n outside indicator. I n a discussion of the sodium thiosulfate titration using starch as a n indicator, Talbot says: “It may perhaps be regarded as the most accurate of volumetric processes.” Treadwell also speaks of i t as “The most sensitive reaction used in analytical chemistry.” He adds t h a t if the water in which the salt is dissolved is free from carbon dioxide, “The solution (of ‘hypo’) can be kept for months without suffering an appreciable change in concentration.” He found t h a t a 2 mo. old solution, one cc. of which was equivalent t o 0.011672 g. of iodine after standing 8 mo., had an iodine equivalent of 0.011667 g. The thiosulfate solution is also easily standardized against the dichromate solution. USE O F METHOD WITH MOHR’S SALT SOLUTION
The following d a t a were obtained by titrating 2 5 cc. portions of a Mohr’s salt solution with 0.09590 normal dichromate until the end-point, using K3Fe(CN)s as a n outside indicator, was reached. Different amounts of potassium dichromate were then added, ammonium fluoride and potassium iodide introduced, and the titration finished with 0 . 0 6 2 1 0 normal “hypo.” The volumes of solution were changed over t o a N / I O basis, and the relation between the excess potassium dichromate taken and the “hypo” necessary t o absorb the iodine liberated is shown in Table I. TABLBI Cc. KKrzOr N/10 0.96 1.92 2.88 3.84 4.80 5.75 6.71 7.67 8.63 9.59
Cc. NazSsOi N/10 0.95 1.90 2.80 3.80 4.70 5.70 6.65 7.65 8.60 9.63
Five different samples of a standard Mohr’s salt solution (0.09650 normal) were then titrated with the standard dichromate, a slight excess of the dichromate solution being added. Ammonium fluoride and potassium iodide were again added and the determination finished b y running a “hypo” titration. The readings were all changed to N / I O and the cc. N / I O Mohr’s salt subtracted from t h e cc. N / I O dichromate, TABLE 11 (C) (A) cc. Mohr’s Salt N/10 15.00 21.14 25.60 30.47 36.42
-
thus obtaining the cc. of N / I O ‘(hypo” which would have been used if there had been no error in the de-
71
termination. The relation of these values t o the volume of “hypo” obtained experimentally is shown in Table 11. The difference in practically every case is very small, and of no quantitative significance. USE O F T H E METHOD WITH I R O N ORES
method was next tried out on a series of I O iron ores. The first method employed used stannous chloride as a reducing agent, and was run as follows: An amount of the ore equivalent t o 2 5 cc. of a N / I O solution is weighed out and dissolved in 2 0 cc. t o 3 0 cc. of I : I HCl by heating on the hot plate for about 2 0 min. Stannous chloride is added t o aid in dissolving the ore. When solution is complete, permanganate is added slowly until a yellow color of Fe+++ appears. Stannous chloride in very slight excess is now added, drop by drop, t o a small volume a t high temperature until the solution is colorless. The solution is then cooled, diluted t o about 2 0 0 cc. and I O cc. of a saturated solution of mercuric chloride is added. An excess of standard KzCrz07 is then run in, and 4 t o 5 g. of ammonium fluoride added. After adding 5 g. of potassium iodide, and allowing i t t o dissolve, the liberated iodine is taken up with standard thiosulfate, The cc. of N / I O “hypo” are subtracted from t h e cc. of N / I O dichromate and the iron calculated. The results first obtained by this method ran uniformly high as is shown in Table 111. STAXNOUS CHLORIDE REDUCTION-The
TABLE I11 KzCrz07 SAMPLE SAMPLE 0.0965 N G. cc. No. 30 l . . . . . 0.6040 2 . .. . 0.5034 20 3. 0.5050 20 4... 0.5040 20 5... . 0.6036 30
. .... .. .
Na2SzOJ 0.1077 N cc. 6.50 2.30 4.00 3.50 11.64
Fe by F e by Regular Modified DichroMethod mate Method Per cent Per cent 20.28 20.11 18.66 18.15 16.57 16.02 17.21 16.58 15.21 14.62
D E T E R M I N A T I O N O F T H E C A U S E S O F T H E INACCURACY-
One cause of these high results was probably the action of the iodine on calomel, oxidizing i t t o the mercuric condition Hg+ I” Hg++ I-.
+
-
+
I n order t o establish this point more definitely, a number of 2 5 cc. samples of a Mohr’s salt solution were measured out and oxidized t o the ferric condition with permanganate, then reduced with stannous chloride, adding different amounts of the salt in excess. These ferrous iron solutions were then analyzed by the modified method as outlined above. The following are su’fficient t o show the results of this investigation: no excess of SnClz Stannous chloride was added until the solution was colorless K2Cr207 = 36.68 cc. N/IOsolution Na2S203 = X I . 6 1 cc. N / I Osolution
I--Practically
Cc. Cc. N/10 “Hypo” (B) NazSzOa Which Should cc. KtCrnOr Actually Used Have Been Used Cc. (B A) Difference N/10 N/10 5.00 $0.07 5.07 20.00 6.72 0.00 27.86 6.72 5.78 +o. 10 5.88 31.38 5.42 +0.02 5.44 35.89 5.15 -0.03 41.57 5.12
2
__-
2 5 . 0 7 cc. N / I OK0-207 to oxidize Fe++ 2-One drop in excess of SnClz KzCr20, = 30. go cc. N / I Osolution NazSzOs = 5 . 6 8 cc. N/IOsolution
25.22 cc. N / I OK2Crz07t o oxidize F e + +
2 72
T H E J O U R N A L OF I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y
3-Four drops in excess of SnCl2 KzCrgOl = 30.90 cc., N / r o solution Na2S20a = 5 . 0 7 cc. N / I Osolution
-
25.83 cc. N / r o KzCrzOlto oxidize F e + + ,+--Eight drops in excess of SnCl2 K2Cr2O7= 30.90 cc. N / i o solution NazSzOs = 3.72 cc. N / I Osolution
-
27.18 cc. N / I OK2Cr20, t o oxidize F e + +
When the potassium iodide is added i t reacts with the Hgff in solution causing the precipitation of red mercuric iodide. This precipitate, however, immediately reacts with the potassium iodide, forming the soluble and colorless Hg14=, which does not interfere with the end-points. The potassium iodide also reacts with the precipitated calomel, changing i t first t o mercurous iodide, which breaks down into mercuric iodide and mercury. 2HgI HgIz Hg This mercuric iodide then dissolves. HgIz 21- + HgI4= As a result of this action there is left only a fine, gray precipitate of metallic mercury which remains during the titration. Other investigators' have called attention t o a similar effect of calomel on the permanganate titration in the Zimmerman-Reinhardt method. Barnebey? states t h a t in the presence of a large amount of chlorides calomel interferes with a successful permanganate titration, and t h a t the end-point becomes more indefinite and transient as the amount of calomel present is increased. Barnebey also states t h a t in some cases the precipitated calomel completely disappeared.
+
+
R E D U C T I O N WITH A M I N I M U M A M O U N T O F S T A N N O U S
CHLORIDE-The analysis of the iron, ores was repeated, using, so far as could be estimated, just enough stannous chloride to reduce t h e ferric iron, leaving practically no excess in solution. Although one ihvestigator could not so regulate the addition of stannous chloride as t o get concordant and correct results, a second analyst handled the method entirely satisfactorily, checking standard iron ores within 0.05 per cent with little difficulty. Some of his results compared with results of the straight dichromate method are given in Table IV. TABLEIV
Fe Fe DifMod- Straight ferqnce ified DichroIn NorNorPer SAMPL .E W T . KzCrzOi, mality NazSrOa mality Method mate Per cent cent Per cent KzCmO? Cc NazSzOa No. SAMPLE c c . 2 0.6000 29.18 0.1030 10.39 0.1010 18.19 18.15 4-0.04 3 0.6000 30.00 0.1030 13.48 0.1010 16.09 16.02 +0.07 4 0,6000 30.00 0 1002 12.45 0.0994 16.42 16.58 +O. 16 I
5 6 7 8 9 10
0.6000 30.00 1 .oooo 30.00 0.5000 18.02 0.5000 19.15 1 .oooo 30.00 0.5000 18.53
0.1002 14.40 0.0994 14.65 0.1002 3.05 0.0994 15.09 0.0986 5.78 0.0989 13.49 0.0986 7.47 0 0989 12.74 0.1002 12.03 0.0994 10.11 0.0986 8.61 0.0989 10.89
14.62 15.12 13.44 12.71 10.01 10.84
+0.03 -0.03 +0.05 +0.03
+o. 10 +o.os
USE O F J O N E S REDUCTOR-when the Jones reductor was used t o reduce the iron t h e method proved t o be entirely satisfactory and correct results were easily 1
p
Meinke, 2.Offenl. Chem., 4, 433. BBmebey, J . A m . Chem. SOC.,86 (19141,1429.
Vol.
12,
No. 3
obtained. The procedure here is very simple. The ore was dissolved in 30 cc. of I : I HC1 without the addition of stannous chloride. It was then diluted to about 150 cc. and reduced b y slowly running through a Jones reductor, taking t h e usual precautions. An excess of standard dichromate was run into the solution, ammonium fluoride and potassium iodide added, and the titration carried o u t as before. The volume titrated was about 350 cc. Definite and permanent end-points were reached. The results may be found in Table V. TABLEV
Fe Modified Dichro0.1028 Normate ORE S A M P L ~ N NarSnOa mality Method No. G. Cc. Cc. NazSaOa Per cent KzCrtO7
1
2 3 4 5
6 7 8 9 10
0.6050 0.6056 0.6046 0.6048 0.6056 0.6043 0.6041 0.6053 1.0050 1.0033
30 30
30 30
30 30 30 30 30 30
9.10 11.28 13.55 12.90 15.05 14.40 16.35 17.22 12.75 11.38
0.0987 0.0987 0.0987 0.0987 0.0990 0.0990 0.0990 0,0990 0.0990 0.0990
20.15 18.18 16.10 16.67 14.70 15.31 13.56 12.70 10.12 10.86
Fe Straight Dichromate DifferMethod ence in Per cent Per cent
20.11 18.15 16.02 16.58 14.62 15.12 13.44 12.71 10.01 10.84
10.04 +0.03 +O.OS +0.09 +0.08 +0.19 +0.12 -0.01 +O.ll +0.02
H Y D R O G E N S U L F I D E REDUCTION-The reduction Of the iron with hydrogen sulfide was found t o be unsatisfactory. The end-point was not permanent, and the results were entirely unreliable. A heavy precipit a t e of sulfur was of course obtained, and this may have been one of the causes of the trouble It was also noticed t h a t a careful regulation of the concentration of Hf seemed t o be essential for a successful reduction of iron.
STANDARDIZATION O F M E T H O D A M O U N T OF SAMPLE-The weight of sample should in each case be such as t o have a n iron content of about 2 5 cc. of a n N / I O solution, or about 0.13975 g. of iron. A M O U N T O F H Y D R O C H L O R I C ACID-when the ore was dissolved in 2 0 t o 3 5 cc. of I : I HC1, concordant results and permanent end-points were obtained. When 40 cc. or more of I : I HC1 were used the end-points were not permanent, the blue color returned and low results were obtained. Too high a concentration of H+ breaks up the ferric fluoride complex and causes iodine t o be liberated, thus giving low results. POTASSIUM IODIDE-Good checks were obtained when 3, 4, 5 , or 6 g. of potassium iodide were added. Five grams is probably t h e most satisfactory amount of the reagent. When stannous chloride is used as a reducing agent, this larger amount is essential owing t o the reaction between Hg++ and the I-. A M M O N I U M FLUORIDE-TWO and three grams of ammonium fluoride gave low results. Four and five grams gave correct, concordant results. Five grams seemed t o be the best amount of t h e reagent t o add. An equivalent amount of hydrofluoric acid can be substituted. V O L U M E O F SoLuTION-The volume of the solution a t the completion of the titrations was about 2 j 0 cc. when the stannous chloride reduction was used. The volume was 350 cc. when the Jones reductor was used. This larger volume was made necessary by the washing of the reductor after reducing the iron.
Mar.,
T H E JOCRiYAL OF I N D U S T R I A L A N D ENGINEERING C H E M I S T R Y
1920
C 0 NCLU SI 0 h'S
The modified dichromate method as outlined above makes use of an exceedingly stable oxidizing salt which can be obtained in a very pure condition. The indicator employed is very delicate and affords an easily obtainable end-point. The method is more rapid than the straight dichromate method, and quite accurate. There seems t o be no reason why i t cannot be successfully used in commercial work. -
I N D I C A T O R S A N D THEIR INDUSTRIAL APPLICATION',2 By H. A. Lubs E. I.
DU
PONTDE
NEMOURS & Co., WILMINGTON, DEL.
Perhaps no single operation of t h e various procedures necessary in general chemical manipulation can be considered of greater importance than t h a t of acidimetric or alkalime tric titrations; yet in spite of this fact the subject of indicators is given but scant attention in the majority of our undergraduate colleges and universities. The most recent and useful developments in t h e field of indicators have arisen from the increasing recognition by chemists and biologists of the great influence which the degree of acidity or H+-ion concentration has upon various biological processes. I n order t o select t h e most brilliant and sensitive indicators for the colorimetric determination of H+-ion concentration in certain biological fluids, Sorensen and his co-workers3 at the Carlsberg Laboratory in Denmark investigated over one hundred dyes, determining the zones over which they changed, their brilliancy, and t h e effect of salt, protein, and protein decomposition products on their changing points. At the same time a great improvement was made in the preparation of standard solutions of known H+-ion concentration for colorimetric work. Some years later Rowntreej4 as a result of his physiological studies a t the Johns Hopkins Medical School, suggested t h e use of phenolsulfophthalein, a compound not described by Sorensen, as a useful indicator for the determination ion of t h e "+-ion concentration of blood. This indicator h a d been synthesized a number of years before by of Remsen, and subsequently studied S ~ h o na, student ~ b y Acree and co-workers from the standpoint of th8 quinone-phenolate theory of indicators. After a careful consideration of the work of Sorensen a n d others on indicators and upon investigating a very large number of compounds, it soon became evident t h a t t h e synthesis of new, brilliant, and sensitive indicators would assist materially in a solution of t h e biological problems in which Dr. W. M. Clark, of t h e Bureau of Animal Industry, and the writer were interested. Having in mind the brilliancy of phenolsulfophthalein and knowing from the quinone-phenolate Paper read a t the 58th Meeting of the American Chemical Society, Philadelphia, Pa., September 2 to 6, 1919. * Published by permission of the E. I. du Pont de Nemours & Co.. Wilmington, Del. * Comfit. rend. trau. Lab. Carlsberg, 1 (1909), 1; 9 (1909), 1: B i o c h e n . Z.,21 (19091, 131, 209, 61 (1913), 307; Ergebn. Physiol, 12 (1912), 393. 4 Archis. I n t e r n . Med., 16 (1915), 38. 6 Am. Chem. J., 20 (1898), 25.7. 1
theory of indicators as developed by Acreel and his coworkers, t h a t by suitable variations in the phenolic residue of a sulfophthalein dye there could be produced great variations in the dissociation constants of this group of indicators, it occurred t o us t h a t the synthesis of new compounds of this type should meet the need for sensitive and brilliant indicators covering a wide range of H+-ion concentration. After about two years of work we were successful in obtaining a series of new and brilliant indicators which left little t o be desired for H+-ion concentration between 10-l and 1 0 - l ~ . This series of indicators and the ranges over which they change is graphically shown in the accompanying chart already published by Clark and the writer.* Reference t o this chart shows t h a t t h e new series covers a range from Ph+I to Pb+IO. The useful working ranges are indicated by t h e heavily shaded portions of t h e curves. Ph' is merely a convenient mode
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