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
the simplest and most desirable way, provided a thoroughly suitable standard substance can be found. Of the indirect methods, the 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 the nitrates. The drying of the deposits presents no special difficulty, but the 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 the 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 the 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 in 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 the 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 the 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 the 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 the 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, thus allowing immediate titration in the cold. 4-It should have a high molecular, or equivalent weight, thus lessening the 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 the 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 tartrate has been strongly recommended by Borntraeger,' and the writer has obtained excellent results with it. Its purification is not exactly easy, but the main objection is its great 1
Zcit. anal. Chem., 26, 334.
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
30
insolubility in water a n d in alcohol, which makes t h e titration tedious. As a n improvement on this, i t seemed t h a t a n analogous compound might be more convenient as regards solubility, a n d t h e acid phthalates appeared worthy of examination. __ T h e acid phthalate of potassium has not apparently been described. It is readily obtained b y half-neutralization of a solution of phthalic anhydride a n d crystallizes nicely in hexagonal plates. ACID P O T A S S I U M P H T H A L A T E
PREPARATION-50 g. resublimed phthalic anhydride are dissolved in about 2 0 0 cc. of water. T h e solution is exactly neutralized with a solution of about 6 0 g. of pure potassium hydroxide in a n equal afnount of water; 50 g. more of anhydride are then added, a n d the heating continued until all crystals are dissolved. T h e solution is now made up t o about 550 g. with water, filtered hot, if necessary, a n d let cool, with continuous agitation t o promote t h e formation of small crystals. When cold, t h e latter are filtered b y suction or centrifuge. T h e yield is about 1 2 5 g. The product is recrystallized from 300 cc. of hot water a n d dried a t 110'. T h e salt is anhydrous KHCsH404 with mol. wt. 204. It is soluble in I O t o 11 parts of water a t ordinary temperatures, a n d in about 400 parts alcohol. This compound seems t o approximate t h e ideal substance, as shown b y t h e following facts:
I-AS regards purity, t h e sublimed anhydride is a n admirable raw material a n d not expensive. Recrystallization of t h e salt is hardly necessary as t h e impurities derived from t h e alkali used should be minimal. a-The salt is stable, anhydrous, not hygroscopic. 3-The solubility in water is sufficient. 4-The molecular weight is higher t h a n t h a t of a n y compound so far proposed, except picric acid. 5-It behaves like a monobasic acid, a n d can be titrated with all desirable sharpness. 6-It is colorless. 7-The writer has found i t t o work well in practice. The acid phthalate of sodium was obtained b y Wislicenus' as a by-product, and described as glassy, prismatic crystals, containing 2H20. Salzer,2 however, reports the salt as anhydrous. It is easily prepared in the manner described for t h e potassium salt, substituting sodium hydroxide or carbonate. I n all cases, however, t h e writer found t h e fine transparent prisms t o contain l/zHzO. The salt is soluble in about g parts water a t 2 5 O a n d analyzed for moist u r e as follows: Wt. of salt
TREATMENT
Time Hrs. 5 (air dry) Desiccator 115 Heated a t 5 0 " C. 24 Heated at 100-1 10' C. 12 1.97 (air-dry) Heated a t 110" C. 12 Moisture calculated for NaHC8HAOa,1/*HsO. , , , Chams -~ ~~
Loss
IN
Gram 0.0055 0.0070 0.2410 0.0950
WEIGHT Per cent
.. , . . , . . . . .. . . .
0.11 0.14 4.82 4.82 4.57
Vol. 7 , No.
I
be used as a standard, b u t t h e potassium salt seems preferable. LABORATORY OF THE DODGE& OLCOTT CO. BAYONNE,N. J.
THE INFLUENCE OF ACIDS AND UPON DETERMINATIONS OF THE CHEMICAL CONSTANTS OF FATTY ACIDS B y C. A. BROWNE Received October 6. 1914
T h e recent paper by Holland' upon "The Determination of the Acetyl Number of Oils, Fats, Etc.," recalls former discussions by Lewkowitsch, Benedikt a n d others regarding the value of the acetyl figure in t h e analysis of f a t t y acids. As t h e author has recently studied t h e determination of t h e acetyl number and other chemical constants in the insoluble acids of several decomposed b u t t e r fats, a few observations upon certain analytical d a t a may possibly be of interest. A serious difficulty, which often confronts t h e chemist in t h e analysis of fatty-acid mixtures, is t h e unstable character of t h e hydroxy-fatty acids. The latter, from their chemical behavior may be divided into two general classes: ( I ) the lactone-forming and ( 2 ) t h e non-lactone-forming hydroxy acids. Lactone-forming hydroxy acids (more especially the y acids) show a pronounced tendency, after being liberated, t o form inner anhydrides. T h u s y-hydroxystearic acid, after separation from its salts or esters, passes immediately into stearo-lactone. C14H29 Cl4H29
I 1 C H2 I CH2 I
I
HCOH
HC--l -
I I CHz I oc--
CHz
I
1 0
+ HzO
OC-OH Hydroxy-stearic acid Stearo-lactone The non-lactone-forming hydroxy acids, on t h e other hand, do not possess the property of yielding inner anhydrides. The hydroxyl group of this class of f a t t y acids remains unchanged and, in distinction from the hydroxyl group of the lactone-forming acids, is free t o react with acetic anhydride during acetylation. This difference in properties of the two classes of hydroxy-fatty acids has frequently been disregarded by chemists in their treatment of t h e subject. It is evident, however, t h a t this factor must play a t times an important p a r t in t h e analysis of complex f a t t y acid mixtures. INFLUENCE
O F HYDROXY-FATTY
ACIDS A N D
LACTONES
O N D E T E R M I N A T I O N S OF T H E ACID, S A P O N I FICATION AND ETHER NUMBERS
T h e salt is t h u s fairly stable u p t o 50'; a t I O O - - ~ I O ~ T h e insoluble acids prepared from t h e ordinary t h e crystals lose 1/2H20 a n d become opaque, b u t re- normal animal fats show usually b u t little difference t a i n their prismatic form. This anhydrous salt may between t h e acid and saponification numbers, t h e ether number in such cases being practically zero. 1 Ann., 942, 89. 1
Ber., 80, 1496.
1
THISJOURNAL, 6 (1914). 482.
