and hydroxylamine as follows. To a solution of nitrite, one-half only of the quantity of sodium amalgam required to reduce it was added, and it was then found to contain hyponitrite and hydroxylamine in the same relative proportion as if the nitrite had been fully reduced (with cooling), and in approximately half the quantities the nitrite would have yielded if the full amount of sodium amalgam had been added.

Sodium amalgam was proved to have little or no action on nitrous oxide by exposing the gas for a long time to its action. The amalgam was liquid, and, when shaken up with the moist nitrous oxide in a stoppered bottle, coated the sides of the bottle. With occasional vigorous shaking, the bottle was kept closed four days; when opened, it was found to contain the nitrous oxide little, if at all, deteriorated as a supporter of combustion. In another similar experiment, a saturated solution of sodium hydroxide was poured over the amalgam ; in this case, the amalgam did not coat the sides of the bottle, but the solution served to keep the dissolved nitrous oxide in contact with the amalgam. The bottle was often vigorously shaken, and was not opened until after four days. The nitrous oxide was almost or quite unchanged. Holt and Sims have studied the oxidation of sodium and potassium by nitrous oxide, but only at much higher temperatures than those in these experiments, which were at 25-30°.

IMPERIAL TOKYO UNIVERSITY, Japan.

XV.-Hyponitrites; their Properties, and their Preparation by Sodium or Potassium.

By EDWARD DIVERS, M.D., D.Sc., F.R.S.

THE hyponitrites have received the attention of many chemists besides myself since their discovery in 1871, and even this year new ways of forming them and the new working of an old method have been published. Yet much has been left to be put on record before a fairly correct and full history of these salts can be said to have been given, and the present paper is meant to be the necessary supplement to what has already been published.

Ways of forming Hyponitrites.

No writer on hyponitrites in recent years has shown himself acquainted with all the known ways of getting these salts, or even with the most productive. The following complete list is valuable,

therefore, and is of special interest as bringing together the various modes of formation of these salts.

1. Reduction of an alkali nitrite by the amalgam of its metal (Divers, 1871).

2. Reduction of an alkali nitrite by ferrous hydroxide (Zorn, 1882; Dunstan and Dymond).

3. Reduction of (hypo)nitrososulphates by sodium amalgam (Divers and Haga, 1885).

4. Reduction of nitric oxide by alkali stannite (Divers and Haga, 1885).

5. Reduction of nitric oxide by ferrous hydroxide (Dunstan and Dymond, 1887).

6. Decomposition of a hydroxyamidosulphonate by alkali (Divers and Haga, 1889).

7. Oxidation of hydroxylamine by sodium hypobromite (Kolotow, 1890).

8. Oxidation of hydroxylamine by mercuric oxide, silver oxide, or cupric hydroxide (Thum, 1893).

9. Interaction of hydroxylamine and nitrous acid (Thum, H. Wislicenus, Paal and Kretschmer, Tanatar, 1893).

10. Oxidation of hydroxylamine by benzenesulphonic chloride and alkali (Piloty, 1896).

11. Interaction, in methylic alcohol, of hydroxylamine with nitrous gases (Kaufmann, 1898, Annalen, 299, 98).

12. Interaction, in methylic alcohol, of hydroxycarbamide and nitrous gases (Hantzsch, 1898).

13. Interaction of dimethylhydroxynitrosocarbamide and alkali (Hantzsch and Sauer, 1898).

Menke's reduction of fused alkali nitrate by iron, and Rây's reduction of mercuric nitrite by potassium cyanide in solution, are not included in the list, because both reductions are very doubtful, and require confirmation before they can be accepted. In the present paper, only the original method of preparing hyponitrites will be treated of.

Preparation of Sodium Hyponitrite Solution by the Reduction of Sodium Nitrite with Sodium Amalgam.

Sodium nitrite can be converted by sodium amalgam in the easiest and quickest imaginable way into fully one-sixth of its equivalent of sodium hyponitrite; this remains in solution, and is pure but for the presence of much sodium hydroxide. From this solution, the sodium salt itself, as well as silver hyponitrite, can be at once prepared, nearly pure and with hardly any loss. The solution, if

cautiously neutralised, is also at once fit for preparing lead, copper, mercury, and some other salts. The neutralisation is known to be complete when a little of the solution just ceases to give black oxide when mixed with a drop of a dilute solution of mercurous nitrate. Others who have tried this method, and particularly Hantzsch and Kaufmann, got far less favourable results.

Pure sodium nitrite is necessary, but that can now be prepared very simply (this vol., p. 85). In order to get as much hyponitrite as possible and as little hydroxylamine, the nitrite must be in concentrated solution; three times its weight of water seems to be the best quantity to dissolve it in when operating in the way to be described. Using these proportions, there is enough water to form, with the sodium oxide produced, a solution of the composition NaOH+3H2O, which is a nearly saturated solution of NaOH,H2O at the mean temperature. In presence of so much hydroxide, the water is also quite saturated with hyponitrite, a small quantity of this salt even separating when the solution is kept at 0° for a time.

To reduce sodium nitrite in cold concentrated solution, 2 atoms of sodium are needed, the additional half atom being consumed in the unavoidable formation of some nitrogen, hydroxylamine, and ammonia. This accords well enough with the statement in my first paper, as a first approximation, that not more than 4 atoms are active on sodium nitrate. In practice, however, 3 atoms of sodium should be used in reducing sodium nitrite, partly because it is wanted afterwards to reduce hydroxylamine, and partly because it is important that all the nitrite should be reduced, and this, notwithstanding statements to the contrary, can only be accomplished quickly in presence of a good excess of sodium. The strength of the amalgam is not an essential point; I have, however, found it most convenient to work with a soft, solid amalgam having the composition (NaHg), or 23 grams of sodium to 1600 grams of mercury. The temperature, also, is not of importance if only the solution of nitrite is concentrated, and although it may in fact rise nearly to 100° without harm, it is better to follow my original direction to keep the flask in a stream of cold water during the reduction. It is, however, preferable to cool it, particularly in warm weather, by means of a brine and ice bath, as then the amalgam can be added much faster without producing any great evaporation. The temperature of the solution during the reduction then ranges, with a convenient rate of

Sodium hydroxide forms a saturated solution at 15° in its own weight of water. When cooled, this solution deposits large pointed prisms of the monhydrate. † Tanatar erred in supposing that I recommended the use of hard amalgam, and his supposed improvement of my process is not one in fact.

working, from 5° to 25°, and the time taken to add 23 grams of sodium need not be more than 10 minutes.

From a quarter to a half gram-molecule of sodium nitrite is a convenient quantity to work on, and the solution is best contained in a 350 to 450 c.c. pear-shaped, wide mouthed flask, lying very obliquely in the cooling bath while the amalgam is added by means of a spatula. The last fourth of the amalgam may be put into the flask as rapidly as it can be, and the flask may then be removed from the bath. It is kept actively rotated for 10-15 minutes, during which the temperature will rise to about 40° and then fall. The solution and mercury are next poured into a narrow mouthed stoppered bottle so as to half fill it, the thick, aqueous solution adhering to the flask being washed into the bottle, but the water used should be limited to 2 or 3 c.c. if it is desired to obtain the solid sodium salt. The whole is now violently shaken for 10 minutes or so, so as to destroy all the hydroxylamine. To ascertain this, a drop of the solution is tested by diluting it and adding a drop of silver nitrate solution, and a slight excess of dilute nitric acid; there should not be the slightest black tint due to silver reduced by hydroxylamine. No gas is liberated during the shaking, but a very strong odour of ammonia is developed. Strange to say, a minute quantity of nitrite is still present, and it seems almost impossible to entirely remove it, although it can be so far reduced by an hour's shaking of the solution with the amalgam that the acidified solution does not blue potassium iodide and starch until it has stood for about an hour.

On separating the solution from the amalgam and exposing it in a dish overnight over sulphuric acid, under reduced pressure, it will be free from ammonia, and is virtually a pure and stable concentrated solution of sodium hyponitrite and hydroxide.

As here described, the preparation of a solution of sodium hyponitrite ready for use is the same as that followed by me in 1871 (with nitrate), except the important modification in the manner of removing the hydroxylamine. When silver hyponitrite is prepared from the crude solution, the hydroxylamine gets destroyed by silver oxide, as I pointed out in the addendum to my first paper. Zorn, as an improvement, introduced the use of mercuric oxide, on the ground that destruction of some silver hyponitrite was thus avoided, but he overlooked the fact that it is the silver oxide, just as it is mercuric oxide, which becomes decomposed, the hyponitrite or any other acid radicle being untouched by the hydroxylamine in alkaline solution. Whether, therefore, mercuric oxide, or silver nitrate, or mercuric nitrate is used, and the precipitated metal then separated, the result is just the same in concentrated alkaline solutions, except that the dropping in a solution of the nitrate is more easy to carry out

than stirring up with mercuric oxide. Further, where the alkaline solution is very weak, the use of mercury compounds is not without objection, as a little mercuric oxide remains in solution. But whether silver or mercury oxide is employed, the result is unsatisfactory, for, as Thum has pointed out, both these oxides, in destroying the hydroxylamine, regenerate nitrite. Not, however, that Thum himself found this prevented him from successfully purifying the silver hyponitrite from nitrite by thorough washing and reprecipitation. Berthelot and Ogier, Paal and Kretschmer, and I myself, have not, however, met with the same success, as I found it necessary, in order to get silver hyponitrite free from all trace of nitrite, to begin by precipitating it in the absence of nitrite. Nevertheless, far from casting doubt on Thum's statement, I believe his silver salt to have been some of the purest ever prepared, from the account he has given of the properties of hyponitrous acid. No one, however, will be disposed to deny the superiority of sodium as a means of removing the hydroxylamine from the solution.

An almost pure solution of sodium hyponitrite can be conveniently got by dissolving the freshly prepared, hydrated, solid salt in water. Sodium iodide, or potassium iodide and the silver salt, will also furnish a solution of alkali hyponitrite. To get a solution for precipitating purposes, Thum proceeded in an indirect way, first preparing a solution of hyponitrous acid, and then adding enough sodium hydroxide to make the solution neutral to phenolphthalein, an effective but very wasteful process. Kirschner also, wanting a solution for precipitating purposes, used sodium chloride and silver hyponitrite, which, in complex and wasteful way, he made to yield a solution which although mixed with much chloride and nitrate, was practically free from silver.

Sodium Hyponitrite.

In 1878, Menke gave full analyses of crystals of a stable salt having the composition of sodium hyponitrite containing 6H2O, which he had prepared by deflagrating in an iron crucible a mixture of sodium nitrate and iron filings, keeping the product at a red heat for an hour in a fire of charcoal rather than of gas, boiling the mass with water, filtering off iron oxide, evaporating, and leaving to crystallise. He makes no reference in his paper to the large amount of sodium hydroxide he must have had to deal with, although this should have seriously affected the procedure. In 1882, Zorn submitted Menke's method to a thorough examination, but failed to obtain the least trace of hyponitrite; he found, however, that ferrous hydroxide, acting on a solution of sodium nitrite, did produce sodium hyponitrite (in solution). His suggestion that Menke had mistaken