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T H E JOCR-VAL O F I - V D C S T R I A L A4VD ENGI+VEERILVG C H E M I S T R Y
general conclusions as t o t h e composition of menhaden oil would not have been changed. As t o t h e usefulness of this method, I know of no other way of determining t h e composition of a mixt u r e of solid f a t t y acids of more t h a n two constituents, especially where only a small quantity is available. Even with large quantities, though it might be possible by means of numerous fractional precipitations or distillations t o separate some of each of t h e constituents in a pure s t a t e , a quantitative result can never be obtained in this way. WYOMING, OHIO
NOTE ON THE DETERMINATION OF STRONTIUM AND LITHIUM IN WATER By S. D. AVERITT Received December 13, 1916
There are probably no determinations in water analysis which on t h e whole require more time and work t h a n those of strontium and lithium. Several years ago while cobperating with t h e Referee on Water -1nalysis for t h e Association of Official Agricultural Chemists. t h e methods which are now official for strontium and lithium were tested. The great amount of time a n d work required for these determinations led t h e writer somewhat later t o inrestigate t h e accuracy of indirect methods which were sound in theory a n d which, with careful work, must prove accurate provided there was a really determinable amount of strontium or lithium present; t h a t is, a n amount that would not be too seriously affected b y t h e experimental error unavoidable in t h e most careful work. This investigation led t o t h e conclusion t h a t t h e indirect methods employed were as accurate as t h e official methods a n d t h e time a n d labor saved was a matter of considerable importance. I t is self-evident t h a t pure preciptates a n d careful work are necessary for indirect methods, t h e lack of which has undoubtedly had much t o do with the unfavorable opinion many chemists entertain relative t o them. I t is believed t h a t a brief statement of the methods will b e of general interest t o water analysts a n d others who have occasion t o determine strontium and lithium, as they differ materially from other indirect methods t h a t have been proposed, a t least in their application t o t h e separation of calcium and strontium and t h e extent t o which they are carried in t h e separation of t h e alkalies. I n t h e brief statement which follows, no details of procedure will be given as they should be perfectly familiar t o any analyst of reasonable experience. The official method (Stromeyer-Rose) for t h e determination of strontium begins with t h e weighed oxides of calcium a n d strontium (CaO and SrO). These are dissolved in nitric acid and brought t o dryness, t h e separation of strontium depending upon t h e insolubility of strontium nitrate in alcohol-ether mixture. The writer’s method is as follows: Dissolve t h e weighed oxides in hydrochloric acid and precipitate again as oxalates as in t h e first case; filter, wash, dis-
Vol. 9, No. 6
solve in sulfuric acid and titrate with standard KMnOa, noting t h e exact volume of K h I n 0 4 required. If T i ’ = weight of CaO a n d SrO. 0 = total oxygen in CaO a n d SrO (found b y t h e titration with KAln04). X = 0 in CaO. Y = 0 in SrO. Then ,Y E’ = 0 (1) and 3.j044X 6.4769Y = T I 7 (2) Solving for Y ,determine SrO (6.4769Y) then W - SrO = CaO. When t h e value of E‘ is found, in order t o get 6.4 7 69SrO a constant factor occurs which is 6.4769 - 3.5044 or 2 . 1 j 9 . Consequently i t is not necessary t o solve these equations in order t o get t h e weight of SrO, which is obtained as follows: - CaO equivalent of K h f n 0 4 titration) 2 . 1 7 9 = SrO. (3) I n order t o test t h e accuracy of t h e above method, pure C a C 0 3 equivalent to 0.9954 g. CaO and S r C 0 3 equivalent t o 0.1000 SrO were dissolved i n hydrochloric acid a n d made up t o 500 cc.; 50 cc. aliquots equivalent t o 0.09954 g. CaO and 0.0100 g. SrO were used, giving t h e results shown in Table I.
+
+
(w
TABLEI-DETERMINATIONOF STRONTIUM (RESULTSI N GRAMS) Expt.
-CaO
+ SrO-
CaO Equivalent
-SrO----.
Found of KMnOd Present A-0. Present 0.1048 0.0100 1 . 0 1095 0.1095 0.1096 0.1052 0.0100 2 0.1095 3 0.1095 0.1096 0 1049 0.0100 4. 0.1095 0.1096 0 1051 0.0100 5(a) 0.1095 0.1097 0 1052 0.0100 ( a ) Precipitated in presence of magnesium chloride.
...... . .
........ .... ...
Found 0.0102 0,0096 0.0102 0.0098 0.0099
The oxalates were washed with a l/2 per cent solution of ammonium oxalate in all cases. Those which were t o be titrated were finally washed with 1 5 cc. of cold water in 5 - c ~ portions . dropped from a pipette around t h e t o p of t h e filter fast enough t o cover t h e precipitate. letting t h e filter run dry between each washing. This amount of washing with water is sufficient for aliquots containing approximately 0.0300 g. of oxides and it is not advisable t o have much larger aliquots for titration nor t o use more water in washing, otherwise strontium oxalate will be dissolved. If t h e double oxides weigh more t h a n 0.0500 g., aliquots should be taken for t h e K M n 0 4 titration. The KMnOl should not be stronger t h a n N/Io. The Official Method for t h e determination of lithium (Gooch) begins with t h e weighed chlorides (NaC1, KC1 and LiC1) a n d depends upon t h e insolubility of sodium and potassium chloride in absolute amyl alcohol. The writer’s method is t o make t h e solution in water of t h e weighed chlorides of sodium, potassium a n d lithium u p t o convenient volume. Take a n aliquot for t h e determination of K from which KC1 a n d t h e C1 in t h e same becomes known. Another aliquot is titrated with standard AgN03 from which t h e total C1 is obtained. If T.T’ = weight of S a C l KC1 LiC1. C = weight of total chlorine (as found b y titration with AgNO3). CZ in NaCl LiCl = C - CZ in KC1. X = Cl in XaC1 and Y = CZ in LiC1.
+
+
+
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(RESULTSIN GRAMS) Lrtxrm Expt. KCI h-aC1 LiCl LiCl NO. Present Found Present Found 1 . . . . . . . . . . . . . . . . .0 . 6 1 0 0 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. KENTUCKY AGRICULTURAL 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
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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.
