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
26
LEAF AND TWIQOILS OF
Digger Lodgepole Red Pine Pine Fir Per cent Per cent Per cent Furfural Trace Trace n-Heptane 3 ... I-a-Pinene ............................... 58-59 3 ? I-Camphene 5-6 1-@-Pinene.. 49-50 16Li8 52 1-Phellandrene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 0 Dioentene .................................. . . . 18 ... ... 1-Limonene ........................... ?.5 ; 3.5 Bornyl ester (as acetate). . . . . . . . . . . . . . . Free alcohol (as 1-borneol). ................ b I .3 7.5 Methylchavicol .......................... ? ? Green oil". ............................ 2-3 -. . . 13 Cadinene . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 Losses by polymerization, etc.. ............. 9 . 5 6 6 FOREST PRODUCTS LABORATORY FORESTSERVICE, U. s. DEPARTWENT OF AGRICULTURE (In CoBperation with the University of Wisconsin) MADISON Constituents Present
.................................... ............................... ................................ ................................
...
...
... ...
THE ELECTROLYTIC SEPARATION OF ZINC, COPPER AND IRON FROM ARSENIC B y A . K. BALLSAND C. C. MCDONNELL Received November 4, 1914
Satisfactory electrolytic methods for the qnantitative separation of zinc and iron from arsenic have not been developed u p t o this time. With respect t o t h e separation of copper from arsenic, several methods are in use, namely, in acid solution according t o Freudenberg,' and in ammoniacal and cyanide solutions as first suggested b y Smith and Frankel,* and M c C ~ ~ . ~ The idea of separating arsenic from other metals b y using an electrolyte of sodium or potassium hydroxide, although by no means novel, has not previously been developed t o a workable basis except in t h e separation of tin and arsenic b y LampBn,' whose work seems t o have been overlooked by more recent writers. A Fischers says relative t o separating zinc from arsenic t h a t it has never been investigated and is only conceivable in an alkaline zincate solution with a definite voltage. The precipitate formed on adding potassium or sodium hydroxide t o the solution of a heavy metal is in t h e case of some metals soluble in an excess of t h e precipitant, forming a strongly alkaline solution from which t h e metal can be deposited by the electric current. Zinc and lead are examples of this, while arsenic, on t h e other hand, exists in solution as a n alkaline arsenate or arsenite, and therefore travels toward t h e anode. With many metals, such as iron and copper, the precipitate is not dissolved by an excess of caustic alkali, b u t its formation may often be prevented by the action of certain organic substances, particularly citric and tartaric acids, and from these solutions t h e metal is easily deposited. Alkaline electrolytes are capable, therefore, of rather wide application. I n this paper we wish t o describe the conditions which were found t o give excellent results in t h e separation of arsenic from copper, from iron, and ,more especially from zinc. Some work is being done upon other metals, notably lead, b u t this is not yet ready for publication. I n all of these separations t h e arsenic must exist 12.physik. 2
Chem., 12 (1893). 117. Amn. Chcm. Jour., 12 (1890), 428. ZtE., 14 (1890). 509. Chcmische Industrie, 1907, 128. Elcctroanalytischr Schnellmethodm. 1908, 246.
a Chem. 4 8
Vol. 7 , No.
I
in t h e higher state of oxidation, otherwise a small quantity will be found in the cathode deposit, and some may also be volatilized. ZINC PROM ARSENIC
It is necessary in connection with our official work in this laboratory t o examine numerous samples of zinc arsenite and products containing it. It was in the course of investigations conducted on methods for analyzing these substances t h a t the following experiments were undertaken. The deposition of zinc from a caustic electrolyte in the absence of arsenic has been so fully discussed b y others t h a t we shall not take it up here except t o s a y t h a t we have found it entirely satisfactory. Since a platinum electrode is injured by t h e deposition of zinc, the cathode used was a nickel dish, preferably with a surface which has been roughened either b y etching or sand blasting. The experiments recorded here were very satisfactorily carried out in ordinary nickel crucibles of about 1 2 5 cc. capacity, offering to8 t h e deposit about g o cm2. of surface. The anode consisted of a No. 14 (B. & s.) platinum wire bent in t h e shape of a flat oval-shaped paddle, whose blade is about 2 . 5 X 2 . 0 cm., and suspended from t h e spindle of t h e rotating mechanism so t h a t t h e paddle blade is just completely immersed in the liquid. This form of apparatus, besides being readily obtainable, has t h e advantage of permitting an unusually rapid agitation of the electrolyte. P R E P A R A T I O N OF soLuTIoNs-For t h e zinc solI?tion a weighed amount of very pure zinc oxide' was.dissolved in dilute sulfuric acid and made t o a definite volume. For the arsenic a solution of pure arsenic acid was used, which was standardized by t h e iodometric method described later. Measured amounts of t h e zinc and arsenic solutions were mixed and sodium hydroxide or potassium hydroxide (50 per cent solution) added until t h e solution became clear, a n d then in excess t o the extent of about 2 0 g. The solution was diluted t o about 95 cc. and electrolyzed. The electrolysis was t h u s started a t room temperature, but the liquid quickly became heated nearly t o boiling. It was found, as mentioned b y Amberg,2 t h a t by using potassium hydroxide decidedly better zinc deposits were obtained t h a n with sodium hydroxide. When sodium hydroxide was used, the deposit frequently showed a tendency t o be spongy, althoygh this could b e remedied somewhat by increasing the rate of anode rotation. The presence of many organic substances in small quantities will also greatly increase t h e adherence of t h e deposit.3 We found t h a t glycerol and a mixture of equal parts of glycerol and alcohol worked very well in these experiments. Even alcohol alone had t h e same effect, but in this case a reddish brown resinous body was formed during the electrolysis. This did not vitiate the results, but rendered t h e siphonate more difficult t o handle. 1 The zinc oxide was analyzed by several methods with the greatest care and found to contain 99.84 per cent ZnO and 0.14 per cent moisture. a B n . , 86 (1903). 2489. 8 Cf. Gmelin-Kraut, "Handbuch der anorg. Chemie." 4 (1). s. 559 rt seg.. (1911).
Jan.;
191j
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 CHEMISTRY
According t o Amberg,’ and Spear and Strahan,2 nitrates should be absent. While we have found t h a t t h e last trace of zinc is deposited very slowly in t h e presence of as little as 0.2 g. KNOI, with such small quantities a particularly smooth and adherent deposit is obtained, and since t h e amount not deposited in a reasonable time should not exceed 0.5 mg., and is usually much less, this error is sometimes allowable. Consequently 0.1 t o 0.2 g. of KNO3 may be added t o t h e solution in order t o improve t h e quality of t h e deposit, without sensibly sacrificing accuracy, unless working upon small amounts of metal or small aliquots. I n general, however, we prefer t h e use of potassium hydroxide, in which case t h e addition of any of these substances is unnecessary. The most prolific source of error in all such determinations is undoubtedly in t h e weighing of t h e large dishes used as cathodes. The following procedure was found satisfactory. The weighings were made with two dishes, one of which was used always as a counterpoise. The dishes, which weighed approximately $ 0 g., were washed with absolute alcohol, dried in the air, heated for half a n hour in a n air oven a t 1 1 0 ’ and placed in a desiccator over sulfuric acid for a t least an hour. They were then removed and weighed immediately. The zinc deposits, after the ’ electrolytes had been siphoned out and replaced by distilled water, were washed well with absolute alcohol, dried in t h e air, heated in t h e oven a t 1 1 0 ’ and weighed as before. It is not necessary t o use ether in drying t h e deposits, nor does any oxidation occur in t h e oven. Zinc deposits heated for 2 4 hrs. a t a temperature of 140’ C. did not show any change in weight. The zinc was dissolved in strong nitric acid and tested for arsenic with ammonium molybdate. For comparison, similar tests were made on solutions containing known amounts of arsenic oxid. (0.1 mg. AssOs was readily detected by this test). I n many zinc deposits no arsenic a t all was found and in no case did i t exceed 0 . 2 mg. Hydrogen sulfide was passed into t h e siphonates from several experiments and t h e amount of zinc shown t o be present never exceeded 0.2 mg. (Such a n amount of zinc in a liter of solution gives a distinct opalescence.) D E T E R M I N A T I O X O F APSENIC-The method employed for t h e determination of t h e arsenic was essentially t h a t of Gooch and Browning3 and was briefly as follows: Evaporate t h e siphonate t o about 2 0 0 cc. and acidify with sulfuric acid, adding 8 t o I O cc. of concentrated acid in excess. Then add 2 t o 3 g. of potassium iodide, a n d boil down slowly until t h e volume is reduced t o about g o cc. Cool t h e solution and destroy t h e iodine remaining by adding sodium thiosulfate solution from a burette. Immediately add sodium bicarbonate i n considerable excess, and titrate with standard iodine. Care should be taken not t o continue t h e evaporation too far, as t h e large amount of alkali salts present may cause t h e solution t o become superheated, with consequent loss of arsenious iodide. 1 LOC.
cit.
* THISJOURNAL, 8
4 (1912). 889. Am. Jour. Science. 40 (1890). 66.
27
Number 1 5 in Table I is t h e analysis of a commercial zinc arsenite. A two-gram sample was dissolved in sulfuric acid ( I t o j), made t o 2 5 0 cc., caustic soda added t o a j o cc. aliquot, t h e arsenic oxidized by warming with a little sodium peroxide, and t h e solution electrolyzed. The results agreed with those obtained by standard gravimetric methods. As lead and zinc are frequently found together in combination with arsenic, a few experiments were made t o see what effect t h e lead would have on t h e procedure. I n an alkaline solution lead separates out on t h e cathode. Cathodic lead tends t o be spongy. Gartenmeister’ has remedied this in a n acid electrolyte by adding gallic or tannic acid. While we have found t h a t t h e same substances will also make t h e deposit from a n alkaline solution smooth, i t is doubtful whether t h e deposited metal is free from organic impurities. If, however, t h e quantity of lead be quite small in comparison with t h e surface of t h e cathode (not more than 0.1 g. metal per I O O sq. cm.) t h e deposit will be satisfactory without t h e addition of any extraneous material. Cathodic lead also oxidizes so readily t h a t i t must be dried with t h e greatest care; b u t if a small quantity of lead is present with a larger amount of zinc, t h e lead deposits first and is subsequently coated by t h e zinc, which prevents its oxidation. The combined deposits are weighed, dissolved in dilute nitric acid and t h e lead determined electrolytically as peroxide.2 If i t is desired t o determine directly t h e zinc, which will be in t h e siphonate from the PbOz, this may be done by driving off t h e nitric acid and again using a caustic electrolyte t o which about j g. of Rochelle salt have been added t o hold up traces of nickel dissolved by t h e acid from the first cathode used.3 Experiment 16 in Table I is a n example of a determination of this kind. To obtain t h e best results a quantity of zinc a t least equal t o t h e lead should be present. A description of t h e conditions employed and examples of t h e results obtained in separating zinc from arsenic are given in Table I . I R O N FROM ARSENIC
Iron deposits free from arsenic from a solution containing a large excess of caustic potash or soda in which precipitation of iron hydroxide has been prevented b y previously adding tartaric acids4 The iron so obtained always contains carbon, unless t h e current is kept below 1.7 amperes per I O O sq. cm. If this is done, t h e amount of carbon present is negligible. The best results are obtained with a current density of less than I ampere per I O O sq. cm. With such a small current, however, t h e deposition is necessarily very slow, and t h e use of a rotating electrode unnecessary. It is often necessary t o run such determinations over night. The iron may be in either t h e ferrous or ferric condition. The apparatus used was t h a t described by Smith.B It consisted of a n ordinary platinum dish cathode and 1 2 8
4
Chem. Zlg., SI (1913). 1281. E. F.Smith, “Electroanalysis,” 5th Ed.. 1911, p. 234. Cf. Vortmann, M o n a f s . , 1 4 (1893). 536. Vortmann, Lac. cif. “Electroanalysis,” 5th Ed., p. 42.
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
28
a spiral anode which could be rotated or not as desired. I n the experiments tabulated below t h e tartaric acid was added t o t h e solution containing a known amount of pure Mohr's salt a n d a definite quantity of t h e arsenic acid solution, a n d this was poured into t h e caustic potash solution. If a precipitate is once allowed t o form it can be redissolved only with t h e greatest difficulty. An excessive amount of sulfate is t o be avoided, as sulfates of t h e alkalis are insoluble in strong caustic solutions. Occasionally, a deposit of iron oxide was observed at t h e anode b u t this can
Vol. 7 , No.
I
copper, t h e precipitation of hydroxide from t h e alkaline solution being prevented b y tartaric acid. T h e copper separating from a caustic electrolyte tends t o be spongy, a n d in order t o get a firmly adherent deposit t h e anode is rotated quite rapidly (1000-1600 R . P. M.) a n d about two grams of potassium nitrate are introduced i n t o the solution. T h e effect here seems t o be, as with zinc, t o decrease t h e rapidity of t h e decomposition while increasing t h e adherence of t h e deposit, b u t all t h e copper can be removed from t h e solution easily in a reasonable length of time. T h e standard copper solution was prepared by dis-
TABLE I-SEPARATION OB ZINC FROX ARSENIC Conditions of electrolysis
Volume of Solution-95 cc. Grams Zn Grams As206 Volts 9.5 4.5 4.0 4.5 4.5
Amps. NDloo 5.5 4.4 2.2 4.0 3.2
Time Min. 90 60 90 70 75
4.0 4.6 4.2 4.5 4.5 5.5 5.0 4.5 4.5 4.0 4.0
2.2 4.4 3.1 4.0 4 0 5.5 5.5 4.4 4.4 2.0 2.2
45 60 70 70 135 135 120 120 60 60
I
No. 1 2 3 4 5
Added 0.3000 0.1989 0.2984 0.2984 0.2984
Found 0.2996 0.1992 0.2985 0.2986 0.2983
Added 0.0500 0.0500 0.1968 0.1968 0.1968
6 7
0.2984 0.2984 0.2984 0.2984 0.2984 0.2000 0.1989 0,1000 0.0995 0.1416(u) 0.1989
0.2980 0.2990 0,2984 0,2989 0.2984 0.2008 0.1992 0.1004 0.0997. 0.1415 0.1991
0.2172 0.2163 0.2088 0.2102 0.2088 . 0.2172 0.2180 0.2172 0,2178 0,5000 0.4995 0.5000 0.5020 0.5000 0.4992 0,5000 0.5009 0.1054(b) 0.1053 0.1968 0.1976
8 9 10 11 12 13 14 15 16
Found 0.0508 0.0498 0.1948 0.1965 0.1962
...
90
Anode rotation, R.P.M 900 800 600 700 600 800 900 700 800 800 1000 900 900 900 600 600
Electrolyte Excess KOH Gms. 20 20
.. .. ..
20 20 20 20
Excess NaOH Gms.
.. ..
21 21 21
.. ..
..
ADDITIONS 3 cc alcohol 3 cc. alcohol 2 cc. alcohol ( 2 cc. glycerol 2 cc. alcohol cc. glycerol 6 . 2 gm. KNOI 0.2 gm. KNOI
(a) Determjnatjon (after removal of arsenic) as carbonate. See Treadwell (Hall), Vol. 11. 3rd Ed., p. 142. ( b ) Determination as pentasulfid. Neher, 2. anal. Chem., 1893, s. 45.
be prevented b y t h e addition of a few cc. of alcohol. As a check on t h e purity of t h e deposit, in a number of cases t h e iron was dissolved in sulfuric acid, reduced with zinc, a n d titrated with potassium permanganate; a n d in other cases dissolved in hydrochloric acid a n d determined as ferric oxide. M a n y iron deposits were tested for arsenic in t h e same manner as t h e zinc deposits a n d more t h a n 0 . 2 mg. of Asz06was never found. TABLE 11-SEPARATION OF IRON PROM ARSENIC Conditions of electrolysis
Volume of Solution-100 Grams iron
No. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
Taken 0.2000 0.2000 0.2000 0.3000 0.2000 0.2000 0.2000 0.2000 0,2000 0 2000 0:2000 0.2000 0.0800 0.0800 0.0800
Found 0.1997 0.2009 0.1996 0.3011 0.1990 0.2004 0.2007 0.2006 0.2011 0.1991 0.2003 0.2002 0.0808 0.0805 0.0806
cc
Grams Ass05
Detd. 0.1998 0.1993 0.1986 0.2996 0.1992 0.1990 0.2001 0.2000 0.1998 0 : 2007 0.1994
....
0.0800 0.0792
Electrolyte Grams
Taken 0.0500 0.0434 0.1086 0.2172 0.1968 0.1968 0.2172 0.2172 0.2172 0.3932 0.3932 0.3932 0.3932 0.3932 0.5000
Found 0.0508 0.0441 0.1084 0.2178 0.1968 0.1968 0.2169 0.2181 0.2169 0.3922 0.3928 0.3927 0.3936 0.3932 0.4993
4& . ;3
g vi
3
1.2 2.4 1.8 2.8 2.8 2.8 2.8 2.5 2.8 0.8 0.8 1.0 0.8 0.8
1.0
0.4 0.8 0.5 0.8 1.7 0.8 0.8 1.3 0.8 0.3 0.3 0.4
0.3 0.3 0.5
."
4 % $c 8m
g#
-4 0 18 0 18 0 18 0 18 31/2 7 00 0 11 0 18 0 18 0 6 0 18 0 13 0 18 0 18 0 20 0 24
28 3 3 3 5 5 5 3 3 3 3 3 3 3 3 3
20 10 20 15 10 10 15 20 20 10 10 20 10 20 20
T h e arsenic was determined iodometrically as' before. T h e presence of tartaric acid does not interfere with t h e titration. Details of t h e method a n d results obtained are t a b u lated in Table 11. COPPER F R O M ARSENIC
T h e same general method applies equally well t o
solving a weighed amount of pure copper sulfate in water a n d making up t o a definite volume. The copper content was verified by a number of electrolytic determinations in both nitric acid a n d potassium cyanide electrolytes. The arsenic solution was the same a s t h a t used in t h e work on zinc a n d iron. The arsenic in t h e siphonate was determined iodometrically, as before. The copper deposits were tested for arsenic with ammonium molybdate, as described previously, a n d t h e y all showed less t h a n 0 . 2 mg. of arsenic pentoxide. The results obtained and details of t h e experiments are given in Table 111. I n general, t h e successful carrying out of these separations depends principally upon having all t h e arsenic in t h e pentavalent form, upon t h e presence of a suficient excess of alkali, a n d upon maintaining t h e conditions which produce a n adherent deposit, Should t h e arsenic be present in its lower form of oxidation i t will invariably contaminate t h e deposit, a n d this will also occur, particularly in t h e case of iron, if too small a n excess of alkali is used. A large excess is always advisable as i t does not exert a n y harmful effect even when t h e electrolysis is unnecessarily prolonged. T h e voltage used does not, as far as we h a v e experimented, have a n y important bearing on t h e results. Except in t h e case of iron, t h e current density may vary between wide limits ; however, i t occasionally happens t h a t when too large, metallic arsenic will separate on t h e anode and finally appear in t h e solution. The time required for a n electrolysis depends very largely on t h e amount of arsenic present, since the arsenates retard the deposition apparently i n
Jan., 1915
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
TABLE I I I ~ E P A R A T I O NOF COPPER FROM A R S E ~ ~ ~ I C Conditions of electrolysis 0
Volume of Solution-100
Grams Cu
No. Taken Found 1
2 3 4 5 6 7 8 9 10 11 12 13 14
0.2061 0.2000 0.2061 0.2061 0.2065 0.2065 0.1993 0.2065 0.2065 0,2000 0,2000 0.2000 0.0800 0.0800
0.2055 0.1992 0.2059 0.2065 0.2061 0.2064 0.1989 0.2062 0.2063 0.2005 0.1994 0.2000 0.0806 0.0796
cc.
Grams AsrOs
Taken 0.0434 0.0500 0.1086 0.1303 0.2088 0.2088 0.1968 0.2088 0.2088 0.3932 0.3932 0.5000 0.3932 0.3932
Found 0.0446 0.0508 0.1078 0.1307 0.2084 0.2088 0.1968 0.2084 0.2090 0.3922 0.3934 0.4993 0.3948 0.3943
n 3 c
2
5.5 4.5 5.2 3.6
...
4.0 4.0 4.0 4.0 4.5 4.8 4.8 4.5 4.5
2 ui a E
4
.-
2d .-**!3
El?
6
E 3;
6.0 4.0 5.8
35 40 30 4...0 40 3 . 0 35 4 . 0 30 4 . 0 20 4 . 5 25 4 . 0 30 4 . 0 40 5 . 0 40 5 . 0 55 4 . 0 30 4 . 0 35
29
t h e simplest and most desirable way, provided a thoroughly suitable standard substance can be found. Of t h e indirect methods, t h e following may be noted:
Electrolyte Grams
PHYSICAL
i
.
Determination of specific gravity.
P
CHEMICAL
%e 8 a 8&
4 1200 1600 1100, 1300 1000 1100 900 1100 1000 1560 1400 1400 1500 1500
w
1
1 1 .2 1 1 0 1 1 1 1 1 1 1
1 1 1
1 1 2 4 1 l/a
1
1
1 1 1
20 10 20 20 20 20 20 20 20 10 10 10 10 10
much t h e same way as t h e nitrates. The drying of t h e deposits presents no special difficulty, b u t t h e weighings should be made with more t h a n ordinary care. CONCLUSION
Zinc, iron, copper, and small amounts of lead have all been successfully separated from arsenic in t h e electrolytic way by using a n electrolyte containing a large excess of potassium or sodium hydroxide. The arsenic is determined in t h e solution from t h e electrolysis. Conditions have been worked out which insure good deposits, and we believe t h a t t h e methods will often greatly simplify t h e course of analysis for many substances containing these metals. INSECTICIDE AND FUNGICIDE LABORATORY MISCELLANEOUS DIVISION,BUREAUOF CHEMISTRY U. S. DEPARTMENT OF AGRICULTURE, WASHINGTON
THE STANDARDIZATION O F ALKALIMETRIC SOLUTIONS By FRANCIS D. DODGE Received October 19, 1914
The text-book methods for determining t h e value of t h e acid and alkali solutions employed in volumetric analysis are not perfectly satisfactory as regards ease and convenience of manipulation. This will be admitted by most technical chemists, and will no doubt account for t h e numerous suggestions which have appeared in t h e chemical literature in recent years and which have as their object t h e simplification or improvement of known processes with respect t o accuracy as well as convenience. Any criticism of these methods is not in relation t o accuracy of results, because i n general t h a t is merely a matter of manipulative skill; but, if one has convenience or economy of time in mind, it would seem t h a t t h e amount of time and care required is disproportionate, or excessive, as compared with t h e theoretical simplicity of t h e end t o be attained. Hence it is presumed t h a t a n account of some attempts made towards this very desirable simplification may be not without interest. All methods so far proposed fall naturally into two classes which can be called direct and indirect. The direct methods involve t h e use of a standard pure substance, which can be weighed with all desirable accuracy and directly titrated. This appears t o be
Gravimetric determination as BaSOd, or AgC1. Electrolysis of CuSO4. Evaporation with " 8 , and weighing ( NH4)2S04. Distillation of "3, etc. Iodometric, involving t h e use of iodic acid and iodates, and thiosulfates. Sodium oxalate, ignited t o carbonate. All these propositions are lacking in simplicity; under special conditions, some of them may, of course, be useful. As already indicated, t h e value of a direct method will depend on t h e availability of the standard substance. A little consideration will show t h a t t h e latter should comply as far as possible with t h e following specifications : I-The standard should be easily obtained in a state of sufficient purity. 2-It should be unalterable in t h e air, a t ordinary or moderately high temperatures, i. e . , neither hygroscopic nor efflorescent. Hence, hydrated compounds are, in general, undesirable. 3-It should be readily soluble in water and alcohol, t h u s allowing immediate titration in t h e cold. 4-It should have a high molecular, or equivalent weight, t h u s lessening t h e effect of small errors in weighing. 5-On titration, no interfering product, as carbonic anhydride, should be present. 6-The standard should be free from color, before and after titration, t o avoid interference with indicators. As far as t h e writer has been able t o ascertain, no standard substance so far suggested answers perfectly these requirements. Brief consideration and criticism of t h e degrees of approximation t o the ideal exhibited by the compounds already proposed are presented below: STANDARD SUBSTANCE FOR ACIDS
1
Equivalent weight
........... ............
Sodiumcarbonate 53 Sodium metal.. 23 Magnesium metal ........... 24 Borax 191 Calcium carbonate (Iceland spar). . . . . . . . . . . . 50
....................
Fails t o pass Specification No. 1 1
2 2
4
5
4
2
5
FOR ALKALIES
Oxalic acid, anhydrous.. . . . . 45 hydrated ................. 63 Acid oxalates.. . . . . . . . . . . . . . . . Succinic acid.. . . . . . . . . . . . . . 59 Malonic acid . . . . . . . . . . . . . . . 52 122 Benzoic acid.. . . . . . . . . . 83 Phthalic acid.. . . . . . . . . . 74 Phthalic anhydride.. 138 Salicvlic acid. . . . . . . . . . . Nitro and amino acids.. . . . . . . . Picric acid. . . . . . . . . . . . . . . . . 2 12 Potassium bichromate.. ..... 146 Potassium bitartrate. . . . . . . 188 Betain hydrochloride . . . . . . . . 153.5
1 1 1
2
4
2
4
2
1
3 3 3 3
....
I
3 1
4 4
6 6
20)
The use of potassium acid t a r t r a t e has been strongly recommended by Borntraeger,' and t h e writer has obtained excellent results with it. Its purification is not exactly easy, b u t t h e main objection is its great 1
Zcit. anal. Chem., 26, 334.
