(NOTE.-See also W. B. Giles, CHEMICAL NEWS, 1909, xcix., pp. 1 and 25, who also obtained some of these results. The present research was completed before we knew of Giles's publication).

It was found to be preferable to lead sulphuretted hydrogen into the warmed ammoniacal solution until it was saturated; the ferrous sulphide thus formed can be filtered much better than when it is precipitated directly with ammonium sulphide.

In presence of a little iron, or if the solution to be filtered is too warm, some of the ferrous sulphide remains dissolved in the ammonium sulphide, forming a green solution. If allowed to stand over-night this dissolved part is also precipitated.

If now the filtrate containing niobic acid is evaporated, when it is sufficiently concentrated, beautiful very silkylooking asbestos-like threads are formed; these dissolve both in oxalic acid and in water. They are double compounds of niobic or tantalic acid with oxalic acid; on evaporating an acid earth solution in tartaric acid these threads are never formed, but if niobic acid is dissolved in oxalic acid and a few drops of tartaric acid are added (which is just enough to stop the precipitation of the acid earth with ammonium sulphide), again on evaporating the same crystals are formed, which proves that the threads are compounds of the acid earth with oxalic and not with tartaric acid.

On igniting these double compounds, pure white leaflets of niobic or tantalic acid remain. The acid earths are obtained in the form of leaflets only when prepared in this way. The acids thus purified are free from iron; they were fused with potassium sulphate, and the solution tested with potassium sulphocyanide, when the absence of iron was proved by the non-appearance of a red coloration.

The ferrous sulphide thus precipitated was free from niobic and tantalic acid, so that this reaction provides a convenient method of quantitatively separating iron from the acid earths. Gooch separated iron from titanium similarly (Zeit. Anal. Chem., 1887, xxvi., 242).

But this method has some disadvantages; for instance, it is not possible by means of it to separate aluminium from the acids, and the decomposition of the oxalic and tartaric acid is in many ways disagreeable. Oxidation with potassium permanganate introduces another troublesome constituent, and it is difficult to evaporate and ignite the residues without loss, while it is necessary to open up the residue again if niobium and tantalum are both present and have to be separated.

If, however, it is only a question of separating quantitatively from iron, this method is the best. Although the acid earths from an analytical point of view resemble iron in many reactions, they also show a close agreement with titanium.

As is well known the most sensitive test for titanium is that with hydrogen peroxide. The titanium compound in question is dissolved in sulphuric acid, and hydrogen peroxide is added when the production of a red or yellow coloration shows the presence of the element. The solubility of precipitated titanic acid in sulphuric acid is, as we have found, much greater if perhydrol is added at the same time; the effect is very marked when ignited titanic acid is being dissolved.

Now the two acid earths either when precipitated or dried, but not when ignited, also possess the property of dissolving easily in acids containing hydrogen peroxide; niobic acid dissolves even more easily than titanic acid, and tantalic acid with more difficulty than the latter.

These solutions of niobium and tantalum are colourless, unlike the pertitanic acid solution; they always contain also higher oxidation derivatives of these elements, for otherwise it could not be explained why a solution containing hydrogen peroxide in alkalis, acids, &c., is not precipitated by any of the reagents which at once precipitate niobic and tantalic acid in absence of hydrogen peroxide. Hydrogen peroxide has the power of rapidly and com pletely dissolving the acid earths which have been separated

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by any precipitating reagent if at the same time ammonia, sodium hydroxide, soda, ammonium chloride, sodium phosphate, or any acid is added. The solvent power is greatest with niobic acid, rather less with titanic acid, and tantalic acid follows last, though even its solubility is very great. From these solutions the acids are not precipitated again until the hydrogen peroxide is decomposed either by boiling or by means of a reducing agent.

A quantitative method of separating niobic and tantalic acid from all other elements is based upon these properties. This separation is effected as follows:

water.

The melt of impure tantalic or niobic acid, prepared with potassium sulphate, for example, is boiled with hot In this liquid are contained as precipitates :— Tantalic or niobic acid, stannic acid, lead sulphate, barium sulphate, strontium sulphate, and calcium sulphate, if it is present in large quantities; the precipitation is, however, not complete, for the solution contains a not inconsiderable amount of the above named acid earths and also the soluble sulphates of other elements.

To the strongly acid liquid (if all the sulphur trioxide has volatilised owing to fusing too long, it is necessary to make it strongly acid with sulphuric acid) some sulphurous acid is added till the liquid smells strongly of it, and it is then warmed. The niobic and tantalic acid are thus quantitatively precipitated, free from iron, manganese, &c. The following results may be taken as an example of the quantitative precipitation of the two acids.

For practical purposes the separation of niobic and tantalic acid from titanium, iron, manganese, lead, and tin are almost the only processes that need be taken into consideration.

The separation of titanic acid will be discussed later. First, experiments will be described which were carried out with solutions of niobium and tantalum, to which large quantities of the elements named were added in order to test the accuracy of the separations. We shall discuss this question more fully when dealing with the investigation of minerals.

For example, ignited niobic and tantalic acid were mixed in different proportions with iron oxide and fused with potassium sulphate. Sulphurous acid was then added to the aqueous extract of the melt, and the liquid was boiled. The precipitated acid earths were filtered, washed with hot sulphuric acid containing sulphurous acid, and a part of the precipitate was boiled with hydrochloric acid; the solution thus obtained was quite free from iron. To test for manganese the same procedure was followed, and the precipitate obtained was examined for manganese after washing with nitric acid and lead peroxide. Moreover, one part of the acid earth obtained by precipitation with sulphurous acid was treated with ammonium sulphide, when the smallest traces of iron and manganese must have been detected by a change of colour of the precipitate.

If the acid earths contain elements which form insoluble sulphates these are found in the precipitate, i.e., with the acid earths. In order to separate them it is only necessary to dissolve the acid earths by means of warm sulphuric acid + hydrogen peroxide-the addition of alcohol in order to separate lead sulphate quantitatively has no effect upon the solubility of the acid earths in the above acid mixture.

With regard to the separation of the acid earths from

RAPID DETERMINATION

OF ASH AND
PHOSPHORUS IN COKE.

By H. M. ULLMANN and N. W. BUCH,
Lehigh University, South Bethlehem, Pa.

THE methods to be described have been found more rapid than the standard method (Fourn. Am. Chem. Soc., xxi., 1116) and other methods in vogue, they are readily carried out with the apparatus and manipulation of common usage, and they can be successfully accomplished by laboratory workers of limited insight. The results attained are constantly accurate, and, indeed, in the hands of hurried or less experienced analysts the results are more accurate and more constant than those arrived at by longer methods exacting more painstaking precautions.

For the determination of ash, 5 grms. of the sample of coke, which has passed a 100-mesh sieve, are weighed out in a previously weighed platinum dish of the usual round bottom shape, of about 150 cc. capacity, or about three and one-half inches across the top. It is advantageous to spread the sample well over the bottom of the dish. From 4 to 6 cc. of alcohol are poured into the dish, and, for a moment, allowed to seep into the coke. The dish is then shaken laterally to promote uniform wetting of the sample, whereupon the pasty mass is made to flow well up on to the sides of the dish by a slow rotary motion, the dish being held at a propitious inclination. With proper manipulation the coke is spread in an even layer over sides and bottom of the dish, and sets in that position due to the slow evaporation of the alcohol. This evaporation may be hastened by blowing on the pasty mass, and if too thick a layer is formed in any one spot, it may be thinned and levelled by blowing at it through a glass tube.

Without waiting for the mass to become absolutely dry, or even for all flow to cease, the dish is placed in a platinum triangle and the residual alcohol is ignited by applying the small smoky flame of a blast-lamp at the top of the dish. As soon as the alcohol has burned off quietly, the dish is heated over the full brush flame of the blast-lamp, the dish being set at such a height that the sides as well as the bottom are heated to bright redness. As incineration progresses the ash flakes off the sides and drops to the bottom of the dish. Complete incineration of a 5 grm. sample is accomplished in twenty minutes. Occasionally specimens of coke have been encountered which show great contraction on ignition. and which have fallen from the sides of the dish before completely incinerated. In these cases the ignition is carried on for a total of thirty minutes; or. if desired, the dish may be rapidly cooled after the first eight minutes of ignition by plunging into water, the halfburned contents again spread with alcohol, the ignition resumed, and the result attained within a further twelve minutes of ignition. The use of absolute alcohol does not secure a compensating advantage. No loss of material occurs during the burning off of the alcohol or as an effect of the air-blast. The rapid combustion is due to a very gentle return eddy of hot combustion products of the Treatblast gases which carry back a supply of fresh air. ment with alcohol and blast repeatedly involves no escape of ash. Attempts to promote a comparably rapid combustion by the use of a muffle with a 5 grm. sample spread

as above have been unsuccessful.

With a 1 grm. sample the above method yields accurate results in ten minutes, and it may be successfully utilised with a 10 grm. sample. A portion of 5 grms. is chosen in our work because it is sufficiently large to avoid the errors due to slate and shale occasionally encountered in I grm. portions; furthermore, a 5 grm. portion is sufficient for subsequent determination of phosphorus. Weighings of dish, coke, and ash for a sample of 5 grms. of ordinary coke may be made rapidly within one-half ingrm., involving an error, at most, of o'or per cent in the result.

To proceed with the rapid determination of phosphorus, the dish is tapped gently a few times to loosen any adhering ash. Ten cc. of concentrated nitric acid are poured

around the sides of the dish, 10 cc. of water are added, and then 3 to 5 cc. of hydrofluoric acid. The dish is covered with a watch crystal, and is evaporated by boiling to a volume of less than 10 cc., or to about 5 cc., requiring about ten minutes. Thirty cc. of hot water are added, the contents boiled for five minutes, and then filtered into an Erlenmeyer flask, washing from four to six times. In a number of cases tried the boiling with water could be omitted and replaced by the simpler addition of hot water and a thorough stirring. Occasionally the first runnings of the filtrate are cloudy, which does no harm; but, if desired, this may be overcome in every case by simply refiltering the first runnings. The above simple and rapid treatment has been found to yield all the phosphorus in a properly oxidised condition, without retention in the residue of calcium phosphate, and without danger of co-precipitation of silico-molybdates.

From this point onward the precipitation and titration progresses by the well-known alkalimetric method for phosphorus. Ammonia is added until a slight precipitate ensues; this is just dissolved with nitric acid; the solution is heated to 85° C.; 50 cc. molybdate solution are added; the flask is wrapped and shaken for five minutes, and then at intervals during ten further minutes. Five minutes of shaking are insufficient with samples of varying phosphorus content; although this shorter time might well yield excellent results in coke from any single source, particularly if the alkaline solution be standardised against a coke of like origin and similar phosphorus content. The precipitate of phospho-molybdate is washed six times with a 2 per cent solution of potassium nitrate, or until free of acid, and is then returned to the flask and titrated with the standard sodium hydroxide solution. This standard solution is conveniently made eqaal to o'00025 grm. phosphorus or o 005 per cent in the 5 grm. sample, and was found to be o 995 of one-fifth normal.

The above methods for ash and phosphorus had proven satisfactory in many specimens of Pennsylvania coke, and we are indebted by the kindness of Prof. N. W. Lord and Mr. F. W. Stanton, of the United States Geological Survey, for twenty samples of coke from various states. Comparative results with the Survey determinations in these samples, calculated to original moisture content, are as follows::

ON THE VOLUMETRIC ESTIMATION OF URANIUM AND VANADIUM.

By EDWARD DE MILLE CAMPBELL and CHAS. E. GRIFFIN.

Up to this time there have been three volumetric methods proposed for the quantitative estimation of uranium and vanadium when occurring together. These methods have all been put forth because of the need for a rapid and accurate method for the analysis of carnotite ores.

The first of these is that of Friedel and Cumenge (Am. Journ. Sci., 1900, x., 135). In this method the ore is dissolved in nitric acid, and the vanadium, iron, and aluminium are rendered insoluble by evaporating to complete dryness. Uranium and the alkalis are extracted by water containing a little ammonium nitrate. The vanadium, in acid solution, is reduced with sulphur dioxide, and the uranium with zinc and sulphuric acid, after which each is titrated with standard permanganate.

A second method is that A. N. Finn (Journ. Am. Chem. Soc., Oct., 1906). The ore is dissolved in dilute sulphuric acid (15), evaporated to fumes, cooled, and diluted. An excess of sodium carbonate is added, the solution boiled and filtered, and the precipitate washed with hot water. The precipitate is re-dissolved in the smallest possible amount of sulphuric acid, and re-precipitated with an excess of sodium carbonate in order to insure complete extraction of the uranium and vanadium. The combined filtrates and wash-waters are slightly acidified with sulphuric acid, 0'5 grm. of ammonium phosphate added, and the uranium precipitated as phosphate by rendering the solution alkaline with ammonia. The solution is filtered, and the uranium estimated by dissolving the precipitate in sulphuric and reducing with zinc. The filtrate from the uranium phosphate is acidified with sulphuric acid, the vanadium reduced with sulphur dioxide, and titrated, like the uranium, with a standard solution of potassium permanganate.

A third method is that of Fritchle (Eng. and Min. Journ., 1900, lxx., 548). The ore is dissolved in nitric acid, diluted with water, sodium carbonate added in excess followed by a large excess of sodium hydroxide. The sodium hydroxide retains the vanadium in solution, but leaves the iron and uranium undissolved. This precipitate, after washing, is dissolved in hot dilute nitric acid, and the iron precipitated with ammonium hydroxide, the uranium being kept in solution by the addition of a large excess of ammonium carbonate. The uranium is reduced with strip aluminium and titrated with permanganate. The precipitate of ferric hydroxide is dissolved in dilute sulphuric acid, the iron reduced with aluminium, and determined with permanganate. In a separate sample the uranium, vanadium, and iron are reduced together with sheet aluminium and titrated with permanganate, the vanadium being calculated from the total amount of permanganate less that required for the uranium and iron. The assumption is made that the amount of permanganate required to oxidise vanadium reduced by sheet aluminium is approximately twice that which would be required if the vanadium had been reduced with sulphur dioxide.

The object of the present research was to devise a volumetric method for the determination of uranium and vanadium in the presence of each other, the method not involving a gravimetric separation of these two elements.

G. Edgar has proposed a method for the differential reduction of iron and vanadium (Am. Journ. Sci., 1908, xxvi., 79), and another for the differential reduction of molybdenum and vanadium (Ibid., 1908, xxv., 332). The iron is reduced to the ferrous condition and the vanadium to the V2O2 condition by the use of zinc and sulphuric acid in a Jones reductor. The reduced solution is caught in a titration flask containing a ferric salt. The solution of highly reduced vanadium reduces the ferric iron to the ferrous condition, and the amount of reduced iron present registers the reduction of the vanadium. The

solution is then titrated as if a solution of ferrous iron alone were to be re-oxidised with permanganate.

The reduction of a vanadium solution to the condition of V2O2 and oxidation in the ordinary way with permanganate always fails to give accurate results, for the reason that the solution of vanadium in this reduced condition has such a strong affinity for oxygen that it becomes partially re-oxidised before the solution can be titrated. The use of the ferric alum as suggested by Edgar prevents this oxidation.

In the experiments tried in the laboratory of the University of Michigan slightly acid solutions of pure vanadyl sulphate and pure uranyl sulphate were used. The uranium solution was standardised by the usual method of precipitation and weighing as U308; also volumetrically by reduction with zinc and sulphuric acid, and titration with standard twentieth - normal permanganate. The vanadium solution was standardised by reduction with sulphur dioxide, the excess of which was removed by the passage of a current of carbon dioxide through the boiling solution, followed by titration with permanganate.

Preliminary experiments were made to demonstrate that sulphur dioxide has no reducing action on uranyl solutions, and that the titration of vanadium solutions when reduced with zinc and sulphuric acid to the V2O2 condition always requires less than three times the number of cc. of permanganate necessary to re-oxidise when reduced with sulphur dioxide. Numerous experiments were made to determine the best conditions for the reduction and titration of uranium solutions.

Belouhoubeck in 1867 proposed the method for the reduction of uranyl solutions by zinc and sulphuric acid, and titration with permanganate. Investigators since that time are much divided in opinion concerning the accuracy of results thus obtained. Some claim that the reduction proceeds further than the UO2 stage, and that the reduced solution needs exposure to the air in order to re-oxidise to the UO2 condition before the titration with permanganate is made. Among those supporting this view are Pullman (Am. Fourn. Sci., 1903, xvi., 229), Goettsch (Journ. Am. Chem. Soc., 1906, xxviii., 1541), and McCoy and Bunzel (Fourn. Am. Chem. Soc., 1909, xxxi., 367). Kern made extensive researches on uranium in 1900 (Journ. Am. Chem. Soc., 1901, xxiii., 685), and shows that the reduction does not proceed below the UO2 stage when sulphuric acid is used, even upon five hours' boiling. All of the above used not less than 50 grms. of zinc, and the ratio of concentrated acid to water varied from 1:6 to 1 : 4.

Kern used sodium carbonate in the titration flask to create an atmosphere of CO2 in order to prevent the oxidation of the uranous solution by air, but Pullman is of the opinion that this means was ineffective, and that the reduced solution was really re-oxidised to the UO2 condition before the titration was made.

In numerous reductions which were made in this laboratory as Kern directs, except that not more than 15 grms. of granulated zinc were used in any one reduction, it was found that results were not very concordant. It was thought that less violent reducing conditions would more easily effect the reduction of uranyl compounds in solutions not so strongly acid.

Reductions were tried on several solutions of uranyl sulphate containing o'1023 grm. of elemental uranium, gravimetrically standardised. In some cases 5 grms. of zinc were used with 5 cc. of concentrated sulphuric acid and 95 cc. of water. The reduction was carried on at a slow-boiling temperature in an Erlenmeyer flask, the mouth of which was closed with a cork through which a small funnel passed. In some cases 2 cc. of free acid were added to 95 cc. of water, and in other cases I cc. was sufficient to effect the reduction. About 5 cc. of concentrated sulphuric acid were added when the reduction was thought to be complete; the solution was cooled somewhat, and was then rapidly filtered through glass-wool to remove undissolved zinc. After dilution to 150 to 175 cc. the solution was titrated with twentieth-normal permanganate.

Results obtained in this way showed but small variation among themselves. The average of a large number gave a uranium content of o 1036 grm., or a positive error of 0'0013 grm. from gravimetric results. The average of a large number of reductions carried on exactly in the way that Kern directs gave a larger positive error than this. Kern states that at least forty-five minutes are needed for the reduction of o'i grm. of uranium solution, but the reduction in the presence of relatively small amounts of free acid was always complete in a half hour, and more often in fifteen minutes on this quantity of uranium, o'2 grm. was easily reduced in this manner in forty-five minutes. The conclusion is that a solution more nearly neutral is more desirable for the reason that it is more rapid, and the results show less variation among themselves. Pullman and others speak of the appearance of brownish colours when the reduction is effected with such

large quantities of zinc and acid. This indicates reduction below the UO2 condition. Working in the presence of relatively small amounts of free acid such colour changes have not been noticed, and this may account for the uniformity in results obtained here, since there is no necessity for the re-oxidation by atmospheric oxygen to the UO2 stage.

Numerous experiments were made with other elements than zinc as reducing agents on mixed uranyl and vanadyl solutions. Among those tried were silver, lead, copper, and aluminium, Kern used aluminium as a reducing agent for uranium (Journ. Am. Chem. Soc., 1901, xxiii., 685), and Fritchle used it for both uranium and vanadium. Silver, lead, and copper offered no advantages which would suggest their use for this purpose. It was thought that some agent might be found which would reduce uranium to the UO2 condition, but at the same time would reduce the vanadium only to the V204 or V2O3 condition. The solution could then be titrated with permanganate in the ordinary way. Since uranium is more difficult to reduce than iron, and since vanadium is much more easily reduced than iron, any agent tried which completely reduced

the uranium was found to reduce the vanadium to such a low state of oxidation that re-oxidation by the air took place before the solution could be titrated. It was thought that possibly the oxygen of the air could be utilised in oxidising the reduced solution to some definite point before titration with permanganate. Experiments were made to test the effect of bubbling air through the reduced solutions, but it was found that conditions of acidity, concentration, and temperature of the solution so influenced the results as to make them unreliable as a basis for a quantitative method.

a

Aluminium offered some advantages over zinc as reducing agent for the reason that it left no residue in the solution, and after reduction is completed the aluminium can be washed free of all adhering liquid very easily. It was effective in the reduction of both uranyl and vanadyl solutions. When strip aluminium was used in an open vessel with mixed solutions of these two elements, 2 or 3 cc. of sulphuric acid being present, reduction proceeded rather slowly. To hasten this process a spiral of heavy aluminium wire, wound to fit a 10-inch test-tube, was used. A mixed solution of uranyl sulphate and vanadyl sulphate was placed in the test-tube, and 50 cc. of water and 5 cc. concentrated sulphuric acid were added. The spiral was dropped in, the solution heated to boiling over the naked flame, and then immersed in a bath of boiling water. The tube was covered with a watch-glass. Reduction began at once, and about five minutes after the lavender colour characteristic of V2O2 had appeared the reduction was found to be complete. The test tube and contents were cooled somewhat by immersion ih running water, then the spiral was withdrawn by means of an aluminium hook fastened to a glass rod. A cc. or two of concentrated sulphuric acid was added, and titration made with permanganate.

Using this manipulation with uranium solutions alone, the following results were obtained :

The calculated number of cc. of permanganate needed This figure for 15 cc. of the above solution was 17:08. was calculated from gravimetric results, weighing as 308, and assuming oxidation to take place on titration from UO2 to UO3.

titrated in the same way, less permanganate than the cal

When vanadium solutions alone were reduced and

culated amount was always needed, and this was the case with mixed solutions of uranium and vanadium.

As the vanadium content was lessened in proportion to the uranium content, the results came nearer the calculated This would be

amount, and became more uniform. expected on account of the strong tendency of V2O2 to reoxidise in contact with air. To prevent this re-oxidation 50 cc. of a solution of ferric alum, made by dissolving 26 grms. of the crystallised salt in a litre of water slightly acidulated with sulphuric acid, were used.

The manipulation was as follows:-The mixed solutions of uranium and vanadium were placed in a 10-inch testtube, 2 to 5 cc. of concentrated sulphuric acid added with 50 cc. of water, the tube heated on the open flame to boiling, then covered with a watch glass, and immersed in a boiling water-bath until reduction was complete as indicated by the lavender or greyish colour of the solution. The tube is cooled in running water until hydrogen bubbles just cease to rise from the surface of the spiral, the spiral drawn to the top of the test-tube with the aluminium hook, 50 cc. of the cold ferric alum solution are poured over the spiral and allowed to mix with the reduced solution, the spiral is drawn out, and the solution titrated with twentieth-normal permanganate in the test-tube until nearly finished; a little free sulphuric acid is added, if necessary, and the solution finished in an Erlenmeyer flask at a temperature of 80°.

Operating in this way the following results were obtained, using 5 cc. uranyl sulphate solution and 5 cc. vanadyl sulphate solution :

The calculated amount of permanganate needed is 18.6 cc. This calculation is based on the assumption that the vanadium is reduced to the V2O2 condition, and requires three times as much permanganate as the same quantity reduced with sulphur dioxide, while the calculation for uranium is the same as in uranium alone above.

Satisfactory results were obtained in this way when the uranium and vanadium were present in equal quantities; when the vanadium is greatly in excess the tendency to re-oxidise is harder to overcome, and the results show more variation.

To apply this method to a carnotite ore the manipulation would be as follows:

0'3 to 0.5 grm. of the ore is dissolved in an Erlenmeyer flask in 40 cc. of 1: 5 sulphuric acid or a mixture of nitric and sulphuric acids, if desired, care being taken to expel all the nitric acid by evaporation. The solution is evaporated until the greater part of the acid is driven off. It is cooled,