MAKE a "prepared " solution of 1 grm. of the substance (2). Just acidify the solution with acetic acid and make slightly alkaline with NaOH. Add 10 cc. each of 2NBaCl2 and 2NCaCl2 (3). Filter (4). Reserve the filtrate for the acids of Groups 2 and 3. Wash the precipitate once with water and transfer to a beaker (5). Treat the precipitate with 45 cc. (1 : 2) HCl (6) and 5 cc. 2N BaCl2. Allow to stand 5 minutes and filter.

Residue

is Filtrate may contain SO3, BO3 (8), C4H4O6 (9), C2O4, F, AsO3 (10), AsO4 (11), PO4, Ca, Ba, and an excess HCl. Add 20 cc. 3 per cent H2O2 (12). Boil the mixture vigorously until all the H2O2 has been decomposed, and filter.

BaSO4 and

Filtrate may contain BO3, C4H4O6, C2O4, F, AsO4, PO4, Ca, Ba, and an excess HCl. Add 2N (NH4)2SO4 (13) drop by drop until precipitation is complete. Boil for one minute, filter while hot on a double filter. Reject residue of BaSO4.

Filtrate may contain BO3, C4H4O6, C204, F, AsO4, PO4, Ca, SO4, and an excess of HCl. Add 5 grms. NH4Cl, dilute to 100 cc. (14), make distinctly alkaline with NH4OH, and filter.

Residue may contain CaC2O4, CaF2, Ca3(AsO4)2, Ca3(PO4)2, and CaSO4 (17). Transfer to a beaker, make acid with acetic, add 10 cc. 36 per cent acetic acid in excess and 5 cc. 2N CaCl2. Filter.

Residue may consist of CaC204, | Filtrate may contain PO4, AsO4, Ca, and an CaF2, and CaSO4. Divide into two equal portions.

excess of acetic acid. Make slightly alkaline with NH4OH, then acid with HCl. Add 2.5 cc. concentrated HCl and 30 cc. H2SO3 (20). Allow to stand 10 minutes in cold. Boil vigorously until all SO2 is expelled. Pass in H2S while hot till precipitation is complete, and filter.

If an estimate of the amount of F is desired the following modified procedure should be employed. The first portion is dried and ignited to convert the CaC204. It is then treated with acetic acid, leaving a residue of CaF2 and CaSO4. It was found that ignited CaF2 was not appreciably transposed by boiling with Na2CO3, while CaSO4 under the same conditions was completely transposed. Accordingly, the residue of CaF2 and CaSO4 is dried, ignited, cooled, powdered, transferred to a beaker, boiled for five minutes with 15 cc. 3N.Na2CO3, and the residue washed by decantation. The residue is again boiled with 15 cc. Na2CO3 solution, the mixture filtered, and the residue washed free of SO4. The precipitate is then treated with an excess of acetic acid. A white residue is CaF2. Confirm by drying the precipitate, transferring to a platinum or lead crucible, and applying the etch test.

19. A rough estimate of the amount of oxalate present can be made by using a standard solution of KMnO4 (1 cc. 10 mgrms. C2O4), and adding the latter drop by drop from a graduated pipette until a faint pink colour persists.

20. H2SO3 is used to reduce the arsenate. The excess of SO2 must be boiled off because the latter reacts with H2S, yielding a precipitate of sulphur, a large amount of which would obscure the test.

21. A precipitate of As2S3 indicates the presence of either arsenite or arsenate. To determine the state of oxidation of the arsenic in the original substance see Note 9.

22. The amount of phosphate present may be estimatcu by adding an excess of (NH4)2M0O4. As this reagent is expensive and the precipitate voluminous it is best to take 1/10 of the filtrate, make it alkaline with NaOH and then acid with HNO3. Add 10 cc. of (NH4)2M004, warm, and allow to stand. The size of the precipitate is a rough measure of the amount of phosphate present.

2N.BaCl2 in a total volume of 25 cc. The mixtures were then centrifuged for two minutes at 3000 R.P.M. and the supernatant liquids poured off. One cc. of dilute H2SO4(3N) was added to each tube and the precipitate stirred up. A drop of o'5 per cent KMnO4 was added to each. The first was not bleached. In the second tube a faint pink colour persisted, while the third remained colourless even after three drops of the KMnO4 were added. The limit of sensitiveness for BaSO3 is therefore 3 mgrms. SO3. By a similar procedure the limit of sensitiveness for CaSO, was found to be 30 mgrms. SO2.

2. The NaASO2 used was found to contain carbonates; hence a different procedure was necessary. By the usual procedure 5 mgrms. of AsO3 gave a cloudiness with BaCl2. Separate solutions, each containing 5, 6, 7, and 8 mgrms. of AsO3 respectively, as NaAsO2 treated in centrifugal tubes with 10 cc. 2N.BaCl2 in a total volume of 25 cc. The solutions were centrifuged for two minutes at 3000 R.P.M. and the supernatant liquids poured off. One cc. each of concentrated HCI and H2O were added to dissolve the precipitate and 10 cc. of a saturated solution of H2S in water. A blank test was run with 1 cc. of a saturated solution containing o'5 mgrm. AsO3 and I cc. concentrated HCl. To the mixture was added 10 cc. of H2S water. The results are given in Table II.

(a)

.

To Determine the Action of Acids upon 500 mgrms. of each of the Acids of Group I. in the Form of their Barium Salts.

Action of Acetic Acid.-Separate solutions, each containing 500 mgrms. of one of the acids of Group I. were treated with 10 cc. of 36 per cent acetic acid and 10 cc. 2N.BaCl2 in a total volume of 50 cc. The solutions were vigorously stirred and allowed to stand five minutes. A precipitate was obtained with CrO4, PO4, C204, AsO3, AsO4, and F. These experiments were repeated, using twenty times the theoretical amount of acetic acid necessary to hold them in solution, but in each of the above cases a precipitate was obtained.

Action of Formic Acid.-The above experiments were repeated using a huge excess of formic acid in place of acetic. The same results were obtained.

Action of HNO3 and HCl.-Upon repeating these experiments with 10 cc. dilute HNO3(3N) it was found that all the above acids were kept in solution. The same results were obtained with 10 cc. dilute HCl(3N).

(b) To Determine the Action of Acids upon 500 mgrms. of the Acids of Group I. in the Form of their Calcium Salts. Action of Acetic Acid.-Separate solutions, each containing 500 mgrms. of one of the acids of Group I., were treated with 10 cc. 36 per cent acetic acid and to cc. 2N.CaCl2 in a total volume of 50 cc. The solutions were vigorously stirred and allowed to stand five minutes. Oxalates and fluorides gave precipitates, the others were kept in solution.

NEWS

Action of HNO3 and HCl.-The above experiments were repeated, replacing the acetic acid by 10 cc. dilute HNO3. Only the oxalate gave a white precipitate. The same results were obtained with 10 cc. dilute HCI. Experiments were then made with the oxalate alone, increasing the amount of HCl or varying its strength as follows:-To a solution containing 500 mgrms. C2O4 as K2C204 10 cc. of 2N.CaCl2 were added. The solution was stirred vigorously and allowed to stand five minutes. The precipitate was filtered off, washed with water, and transferred to a beaker. A solution of HCl of definite concentration was added, I cc. at a time, till the precipitate was completely dissolved. The results obtained are given in Table III.

Conclusion. (a) All the acids of Group I., with the exception of sulphates when precipitated by a mixture of BaCl2 and CaCl2, may be readily taken into solution with 40 cc. HCI (1:2). In the scheme 45 cc. are used to insure a slight excess of HCl. (b) Acetic acid (10 cc. 36 per cent) may be used to separate oxalates and fluorides from borates, tartrates, chromates, phosphates, and arsenates, when these acids are precipitated as calcium salts. Since the Ba salts of these acids are not similarly affected by acetic acid it is necessary to remove the Ba by precipitation with a sulphate before the above separation can be made.

III.-To Determine the Minimum amounts of CaC204 and CaF2 which may be respectively precipitated by CaCl2 in a Definite Volume in the presence of 10 cc. 36 per cent Acetic Acid.

A

(a) To a solution containing 1 mgrm. C2O4 as K2C2O4 were added 10 cc. of 36 per cent acetic acid and 10 cc. of 2N.CaCl2 in a total volume of 50 cc. The solution was heated to boiling and allowed to stand ten minutes. white cloudiness was obtained. (b) To separate solutions, each containing 1, 2, 3, 4, 5, and 10 cc. respectively of F as NaF, 10 cc. of 36 per cent acetic acid and 10 cc. 2N.CaCl2 were added in a total volume of 50 cc. The solations were heated to boiling and allowed to stand ten minutes. Negative results were obtained with 1-3 mgrms. F. With 4 mgrms. F a faint cloudiness was obtained, while 5-10 mgrms. F gave a decided cloudiness. (To be continued).

THE CONSTITUTION AND STRUCTURE OF AN ATOM OF NITROGEN.

By HAWKSWORTH COLLINS.

SIR E. RUTHERFORD has lately described experiments, from which he deduces that an atom of nitrogen is probably disintegrated. in such a manner as to produce two atoms of hydrogen and a mass of 12.

In 1914 a mathematical proof that an atom of nitrogen is constituted by the union of two atoms of hydrogen with one of carbon was sent to the Nobel Institute of Sweden.

If Sir E. Rutherford's deduction turns out to be true this will be at least the fourth confirmation by direct experiment of a "Theory of the Constitution and Structure of the Chemical Elements," which was first produced in 1903.

The three other important confirmations are as follow:

In 1911 the discovery of the exact relative volumes of the elements to two decimal places was made, the results bearing no resemblance to those of Kopp or of any other scientist, and were obtained from experimental data without the assistance (?) of any hypothesis whatever.

The results which concern the atom of nitrogen, and which were demonstrated in full in the communication to

the Nobel Institute, are as follow:

1. The relative volume of an atom of carbon at 15° C. in all carbon compounds in which the element is united only by single bonds to other elements is o'71.

2. The relative volume of an atom of hydrogen at 15° C., when united to an atom of carbon in one particular position, which is called "the first position," is always

15.25.

3. The relative volume of an atom of hydrogen at 15° C., when united to an atom of carbon in another particular position, which is called "the fourth position," is always 5.76.

4. The relative volume of an atom of nitrogen at 15° C. when united only by single bonds to other elements, is 0.71.

5. The relative volume of an atom of nitrogen at 15° C., when united to an atom of carbon by three valences and in some other cases, is 15.96=0'71+15:25.

6. The relative volume of an atom of nitrogen at 15° C. in nitrates, nitrites, &c., is 21'72=0'71+15.25 +5.76.

No one could possibly have guessed or hypothesised such a state of affairs, and then manipulated thousands of experimental data so that they fall into line in support of the hypothesis.

The above results show that two of the "hydrogen" constituents of nitrogen are capable of being expanded from negligible volume to 15.25 and 5'76 respectively.

If this represents the constitution and structure of an atom of nitrogen in the gaseous state, it is not surprising that collision with an a-particle should tear the two H-atoms from the main mass, for the volume occupied by these two constituents of nitrogen is about 30 times the volume of the remaining portion. The action would be comparable to the tearing away of a balloon by a sudden gust of wind from the hands of those who were holding it; the great strain on their arms being too sudden to given them an opportunity of overcoming the inertia of their bodies.

As several portions of the above-mentioned theory have now been proved to be true by direct experiment, it is practically certain that the whole of it is true, and that therefore, if scientists would make a serious study of it, further discoveries by direct experiment with regard to the constitution and structure of the chemical element would be facilitated.

solution with a 10 per cent solution of nitric acid. The concentration of the acid in the cup was kept approximately constant during the electrolysis by fitting the cup with a constant-level syphon, and slowly dropping distilled water into the cup during the run. Agitation of the mercury cathode and of the solution was effected by air blown through glass tubes that dipped below the surface of the mercury. One cell was provided with two such air jets, the other with twelve. A sheet of platinum, inserted in the porous cup, served as anode.

The electrolysis was begun immediately after the porous cups were put in place and the anodes inserted. A current of three amperes was used and the electrolysis was continued until the amount of the hydroxides desired for the fraction had been precipitated.

The hydroxides precipitated in the two cells were distinctly different in character. Where the stirring bad been slight, the hydroxides were granular and were easily collected on a filter. The precipitate in the cell in which the stirring had been vigorous was very finely divided, and could rapidly be separated from the liquid only by filtra

In a previous article upon this subject (Dennis and van der Meulen, Journ. Am. Chem. Soc., 1915, xxxvii., 1963; CHEMICAL NEWS, cxix., 1) the fractional precipitation and separation of the rare earths by the electrolysis of aqueous solutions of their salts at voltages considerably higher than the decomposition values of these compounds were explained as probably due to the action of the hydroxy! ions, concentrated near the cathode, upon earths of different basicities, the hydroxide of the weakest base being precipitated first. If this explanation is correct, it follows that the selective precipitation of the hydroxides in the order of the basicities of the earths should proceed more evenly, and the separation of the earths be more complete, as the vigour with which the electrolyte is stirred is increased, because this would bring the bydroxyl ions more frequently into contact with the weakest bases and would thus tend to lessen the simultaneous precipitation of hydroxides of earths of different basicity.

With a view to gaining experimental evidence upon this point, two portions of a solution of certain rare earths were electrolysed under identical conditions, except that one solution was vigorously stirred, whereas the other was agitated just rapidly enough to keep the surface of the mercury cathode free from adherent deposit of the precipitated hydroxides. (For detailed description of the apparatus that was used for the electrolysis see Dennis and van der Meulen, loc. cit.).

The mixture of rare earths that was employed contained the yttrium and erbium groups and a trace of neodymium, but was free from thorium, cerium, and the more common elements. The average atomic weight of the earths in the mixture was 106 95. A neutral solution of the nitrates of these earths was prepared and was diluted with water until it contained 34 grms. of oxides to the litre. Two portions of this solution, of five litres each, were used for the electrolyses. The containers for the solutions were glass cylinders about 20 cm. in diameter. A layer of mercury about 15 cm. deep, which served as cathode, was placed in each cylinder, and this was covered with 5 litres of the solution of the earths. A porous cup 6 cm. in diameter and 15 cm. deep was suspended in the electrolyte and was filled to within one cm. of the height of the outer

of suction. Moreover, the precipitated hydroxides from this second cell were dark in colour because of the presence of finely divided mercury. We observed no indication of the formation of an amalgam of the rare earths, thus confirming the statement of Kettembeil (Zeit. Anorg. Chem., 1904, xxxviii., 213).

the

When an amount of the rare earth hydroxides desired for one fraction had been precipitated, the current and air blast were turned off, and the porous cups were removed from the cells. The solution in each cell was syphoned off and was then filtered on a Büchner funnel to remove the suspended hydroxides. The mercury and hydroxides still remaining in the cell were transferred to a separatory funnel, the mercury was drawn off, and the hydroxides were then brought upon the filter. The precipitate was thoroughly washed with water and was then treated with warm 2 Ń hydrochloric acid, which quickly dissolved the hydroxides but left most of the finely divided mercury undissolved. Hydrogen sulphide was passed through the filtrate to remove the slight amount of mercury that had been dissolved, the solution was again filtered, the hydrogen sulphide was removed by boiling, and the rare earths were precipitated by oxalic acid. The oxalates were washed with hot water until free from chlorides and were then dried at 100°.

The residual solution from which the precipitated hydroxide has thus been removed, together with the wash water which had been evaporated to small bulk, were returned to the cell and the electrolysis was continued until a second fraction of the rare earth hydroxides had been precipitated. This precipitate was removed and purified as before, and electrolysis was repeated until nine fractions had been obtained. The rare earths still remaining in solution were then precipitated by oxalic acid.

The atomic weight of each fraction was determined by the oxalate-oxide method. The absorption spectrum of each fraction was studied with the aid of a Krüss spectroscope, and the relative intensities of distinctive bands were approximated by the method of Dennis and Bennett. (Fourn. Am. Chem. Soc., 1912, xxxiv. 7). A neutral solution of the chlorides of the earths, containing 5 grms. of the oxides in 25 cc., was employed in each spectroscopic

examination.

The data obtained in these two series of electrolyses are given in Tables I. and II.

The atomic weights of the various fractions and the relative intensities of the distinctive absorption bands of the "coloured" earths in the fractions are plotted in Figs. 1 and 2. The spacing of the fractions along the axis of abscissas is based upon the actual weights of the several fractions.

Comparing the results of the two series of electrolyses it will be noted that as the vigour of stirring of the catholyte is increased, there results a somewhat more rapid