June, 1917
1 H E J O C R N A L 0F IiV D U S T RI A L A N D E nTGILVE E RI llr G C H E M I S T R Y
+ +
S Y = C - Cl in KC1 (I). Then, 1.6486X I . I g j 7 Y = W - KC1 ( 2 ) . and Solving for Y find weight of LiCl (1.1957Y) in getting t h e weight of LiCl from Y a constant factor occurs, v i e . , I .192-_ or 2.64, a n d as in t h e case of strontium 1.6486- 1.1957 it is not necessary t o solve t h e equations. T h e weight of LiCl is obtained as follows: The NaCl equivalent of C - CZ in KC1 - ( W KC1) multiplied b y 2 . 6 4 = LiCl (3). I n order t o test the accuracy of t h e method, 0.5000 g. NaC1, 0.1000 KC1 a n d 0.0100 LiCl were dissolved i n water a n d diluted t o I O O cc. Spectroscopic tests showed a small quantity of potassium in t h e sodium chloride and a trace of sodium in t h e potassium chloride. This was immaterial since no lithium was shown in either t h e sodium chloride or potassium chloride nor was there a n y lithium in t h e calcium and magnesium chlorides used, b u t a small quantity of sodium a n d a trace of potassium were indicated in both. The results appear in Table 11.
TABLE11-DETERMINATION OF LITHILW(RESULTS IN GRAMS) Lrtxrm Expt. KCI h-aC1 LiCl LiCl NO. Present Found Present Found 1 . . . . . . . . . . . . . . . . .0.6100 0.6098 0.0101) 0.0106 2 ( a ) . . . . . . . . . . . . . .0.1525 0.1569 0,0023 0,0025 ( a ) Determination in a solution containing calcium and magnesium chlorides
+
+
The determination of lithium by this method is based upon two other definite determinations, potassium a n d chlorine, t h a n which, in t h e hands of a skilful analyst a n d under t h e conditions of this method, no determinations are more accurate. T h e only other factor affecting t h e accuracy of t h e method is a n impurity in t h e weighed chlorides and under ordinary conditions this can result only from careless work or inexperience. KENTUCKYAGRICULTURAL EXPERIMENT STATION LEXINGTON, KENTUCKY
NITRATE DETERMINATIONS IN THE PRESENCE OF
CHLORIDES By W. F. GERICHE
Received February 2, 1917
T h e presence of chlorides in solutions on which nitrate determinations are t o be made by t h e colorimetric method has long been a source of trouble t o t h e analytical chemist. When nitrates are present in large amounts in solutions containing chlorides, determinations can very easily be made b y t h e use of some of t h e reduction methods. Since, however, determinations for nitrates are often called for in solutions i n which t h e amounts present are small, the quantity of ammonia produced by t h e reduction of t h e nitrates is of such magnitude as t o often introduce It is a considerable error due t o manipulation. under such conditions t h a t t h e phenoldisulfonic acid method for nitrate determination is often employed, a n d in t h e absence of chlorides has been found t o be sufficiently accurate a n d expeditious. T h e effect of chlorides on nitrate determinations has been t h e subject of some s t u d y a n d has been duly reported in chemical papers. It is not deemed necessary t o review here t h e literature on t h e subject. Suffice
585
i t t o mention some of t h e results of the more important investigations. ( I ) Chlorides cause losses of nitrates in determinations made b y t h e phenoldisulfonic acid method. ( 2 ) The loss of nitrates is not occasioned b y t h e evaporation of t h e aqueous solution t o dryness prior t o t h e addition of t h e phenoldisulfonic acid. (3) The loss of nitrates occurs when t h e phenoldisulfonic acid is added t o t h e residue from t h e evaporated solution. (4) T h e use of precipitants t o remove t h e chlorides prior t o t h e evaporation of t h e aqueous extract is recommended for accurate determinations. ( 5 ) T h e use of calcium oxide a n d also calcium carbonate for t h e clarification of aqueous extracts, especially from soils, is recommended as a precipitant t h a t is both efficient a n d non-interfering in t h e nitrate determinations. The result of investigations, t h e conclusions of which have been briefly stated above, indicates t h a t t h e presence of chlorides interferes with t h e reactions a t a certain point in t h e process of the determinationsnamely, when t h e acid a n d dry salt containing t h e nitrates a n d chlorides come into contact. This results in t h e production of heat with t h e liberation of both chlorine a n d nitric acid, a n d t h u s interferes with t h e proper reaction of t h e latter with t h e phenoldisulfonic acid. Working on the principles enunciated by the investigators studying t h e colorimetric method of nitrate determinations, i t occurred t o me t o t r y a method b y which total evaporation of t h e nitratebearing solution t o dryness could be obviated together with t h e necessity of adding t h e acid t o t h e dry residue. Since t h e phenoldisulfonic acid reagent is a mixture of sulfuric acid and phenoldisulfonic acid i t seems t h a t t h e proper condition for t h e reaction of t h e phenoldisulfonic acid a n d t h e nitrates is in a sulfuric acid solution. By t h e addition of sulfuric acid t o t h e nitratecontaining solution, a condition is brought about by which t h e complete evaporation t o dryness of t h e aqueous solution may be obviated. When t h e phenoldisulfonic acid is then added t o t h e acid-treated nitrate solutions some nitrophenoldisulfonic acid is formed. T h e complete reaction, however, will t a k e place when t h e proper concentration of t h e solution has been attained. T o attain this concentration a n d t o employ temperature t o accelerate t h e reaction of t h e nitrates a n d t h e phenoldisulfonic acid is t h e purpose of t h e partial evaporation t o which t h e samples are subjected. I n making nitrate determinations one must remember t h a t t h e theoretical reaction t h a t elucidates t h e principle of t h e method goes t o completion for quantitative determination only when a n excess of phenoldisulfonic acid is used. Therefore, proper care should be taken in t h e preparation of t h e sample t h a t t h e amount of nitrate present in t h e sample be neither too large nor too small t o introduce measurable error due t o t h e excessive or insufficient use of a given measure of t h e required acid reagents. Too much acid may seriously affect t h e accuracy of t h e determinations of samples in which t h e nitrate content is small.
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T H E JOURNAL OF INDUSTRIAL A N D ENGINEERING CHEMISTRY
because of t h e action of t h e acid on t h e salts, and t h e increase in temperature involved. The phenoldisulfonic acid reagent, as used in t h e laboratory, was prepared according t o t h e Chamot method, i. e., a n addition of fuming sulfuric acid is employed t o insure pure phenoldisulfonic acid, free f r o m all traces of phenolmonosulfonic acid. T h e quantity of t h e sample used for analysis must be determined by t h e amount of nitrates in t h e aqueous solution. If t h e nitrate content is from I t o j parts per million, a sample of a t least j o cc. should be used. To t h e sample, placed in a casserole or beaker, 1 . j cc. of concentrated sulfuric acid are added with constant stirring, then z cc. of phenoldisulfonic acid reagent. T h e casserole is then placed on a water b a t h , a n d most of the solution evaporated a t t h e ordinary temperature of t h e steam bath. The last part of t h e evaporation, however, should be performed at a temperature preferably not over 7 0 ' C. T h e evaporation should proceed until t h e original solution is concentrated t o a quantity varying from 6 or 7 t o 1 2 or 14 cc. The point t o which evaporation must be continued is determined b y t h e amount of nitrates in t h e original solution; for a low nitrate cont e n t a greater concentration of t h e original solution will be necessary. T h e proper concentration is determined by t h e color of t h e solution, which resembles t h a t of phenoldisulfonic acid, slightly tinged with yellow. This condition will come, and final evaporation be attained a t about t h e time t h a t acid, due t o t h e presence of chlorine, can be detected in t h e evaporating vapors. T h e important thing t o observe in this modification is t o bring about t h e final evaporation a t a relatively low temperature. I n no case should t h e solution be materially colored and turbid, although i t may be somewhat darkened. X colored solution will result in a n off tint when t h e alkali is added a n d will necessarily interfere with t h e accuracy of the determination. When t h e evaporation of t h e solution t o its proper concentration has been accomplished, about 50 cc. or more of mater are added; t h e solution is t h e n neutralized with a n alkali, care being taken t o avoid t h e formation of excessive temperature when t h e acid is neutralized. T h e solution is then placed in t h e colorimeter a n d compared with a standard previously prepared, which may be made up according t o t h e old method of total evaporation t o dryness before adding t h e reagents, or according t o t h e modification here reported, either of which will give t h e proper tint. R E S U L T S OBTAIKED
Table I indicates t h e feasibility of adding t h e phenoldisulfonic acid reagent before evaporation t o dryness. Table I1 indicates t h e practicability of t h e method even if relatively large amounts of sodium chloride are present. If t h e nitrate content is very low and t h e salt very high, for instance, I part per million of nitrate and I per cent NaC1, determinations were subject t o serious errors, due t o loss of nitrates a n d discoloration of t h e solution. I n cases of very low nitrate and high salt content, evaporation of t h e solution t o its proper concentration should be performed a t a much reduced
Vol. 9, NO. 6
TABLE I 5 0 cc. Solution in Sample 1.5 cc. Sulfuric Acid Added 2 cc. Phenoldisulfonic Acid Added liimrc Theoretical ACTUAL READING CHANGE NITROGENAmount in cc. in cc. of IN P . p. m. of Standard Standard TINT 1 50 49 None 1 50 50 None 2 100 100 None 2 100 98 None 5 500 500 None 5 5 00 500 None 20 1000 1000 None 20 1000 1020 None TABLEI1 50 cc. Solution in Sample Theoret- Amount NITRIC ical Re. h-ITROSaCl Per cent Amount covered GEN Added in Cc. of NaCl (CC. of P. p. m. mg. Standard Present Stan.) 1 100 0.1 50 50 100 0.1 1 50 50 I
I I 1 1 1
1 1 5 5 IO 10
250 250 500 500 750 i50
1000 1000 500 500
1000 1000
0.25 0.25 0.50 0.50 0.75 0.75 1 .oo 1 .oo 0.50
0.50 1.00 1.00
50 50 50 50 50 50 50 50 250 250 500 500
50 48 49 50 50 46 35 30 250 250 500 500
CHANGE IN
TINT None
None Slightly colored Colored Badly colored Badly colored None None . .-. None None
temperature and preferably under partial vacuum, in order t o reduce t h e action of acids on t h e salts. SUMMARY
I--\ satisfactory modification of t h e phenoldisulfonic acid method of nitrate determination in presence of chloride salts has been found. 11-Total evaporation of t h e solution t o dryness can be obviated by t h e use of concentrated sulfuric acid, which is added t o t h e aqueous extract. 111-The addition of sulfuric acid a n d phenoldisulfonic acid t o t h e aqueous solution prevents t h e loss of nitrates, which in t h e old method was due t o t h e action of acid added t o t h e dry salt after evaporation t o dryness had been accomplished. IY-The temperature at which t h e final evaporation and concentration of t h e aqueous solution is performed should not exceed 70' C. SOILCHEMISTRY LABORATORY OF CALIFORNIA, BERKELEY UXIVERSITY
A NOTE ON THE PHENOLSULFONIC ACID METHOD FOR NITRATES IN WATERS HIGH IN MAGNESIUM SALTS By M. STARRNICHOLS Received February 28, 191;
I n t h e phenolsulfonic acid method for t h e determination of nitrates in water supplies, as given in t h e "Standard Methods of Water Analysis of t h e American Public Health ,ksociation," no provision is made for t h e removal of t h e hydroxides of magnesium a n d iron which may form on t h e addition of t h e alkali hydroxide used t o neutralize t h e excess phenolsulfonic acid. I n this laboratory. until recently, t h e colored solution containing t h e nitrated sulfonic acid has been filtered t o remove these hydroxides a n d t h e filter paper subsequently washed. I n t h e absence of t h e hydroxide of iron, t h e filtration may be dispensed with a n d t h e color read immediately if a quantity of a n ammonium salt is added t o hold t h e magnesium in solution. There are two
