Chapter 11

When it is desired to make a determination of nitric acid, 100 c.c. of solution No. 1 are measured off, and as much of it as may be convenient is poured into the tubes, E, E, together with about a gramme of zinc sulphate for each tube, which substance appears to considerably facilitate the absorption of the nitric oxide by the permanganate. When the operation is over, the contents of E, E are poured into a beaker glass. 100 c.c. of solution No. 2 are then measured off, and a portion, together with a little sulphuric acid, poured into E, E, to dissolve the oxide of manganese which has separated during the absorption of the nitric oxide. The oxide having been dissolved, the liquid in E, E, and the rinsings of the tubes, also the residues of permanganate and oxalic acid left in the measuring flasks, and the rinsings from these, are all brought together in the same beaker glass. Finally, the amount of solution No. 3 required to decompose the excess of oxalic acid is determined. If we subtract from the amount thus found the quantity of permanganate required to equalize solutions Nos. 1 and 2 (previously ascertained), we shall have the amount of permanganate actually reduced by the nitric oxide, according to the reaction:

6KMnO_{4} + 10NO = 3K_{2}O + 6MnO + 5N_{2}O_{5};

in other words, on the basis that one molecule of potassium permanganate will oxidize one and two-thirds molecules of nitric oxide:

(KMnO_{4} = 1-2/3 NO).

The method of using the apparatus is simple. The nitrate is placed in B, and the joints made tight, except that at _f_, which is left open. A current of carbon dioxide is passed through the apparatus until all of the air has been displaced. Connection is then made at _f_, and soon afterward the current of carbon dioxide is shut off at _d_.

The flask, B, is now heated as long as may be necessary in order to produce, on cooling, the diminished pressure required for the introduction of the ferrous chloride and hydrochloric acid. Before removing the flame, the joint at _f_ is closed to prevent the return of the permanganate solution.

As soon as the flask, B, has become sufficiently cool, the ferrous chloride and hydrochloric acid are introduced through the tube, _a_ (which has been full of water from the first), in the same manner and quantities as in the well-known Tiemann-Schulze method.

The pinch cock at _d_ is then opened, and the apparatus allowed to fill with carbon dioxide. When the pressure has become sufficient to force the gas through the solution of permanganate, the pinch cock at _f_ is removed. It should be opened only slightly and with great caution at first, unless one is certain that the pressure is sufficient. If the pressure is insufficient, the fact will be made apparent by a rise of the permanganate in the small internal tube.

The flow of carbon dioxide is now reduced to a very slow current, or entirely cut off. The contents of B are slowly heated, until the decomposition of the nitrate is complete and the greater part of the nitric oxide has been expelled, when the apparatus is again closed at _f_ and _d_, and allowed to cool. The tube, _a_, is then washed out, by the introduction through it into B of a few cubic centimeters of strong hydrochloric acid.

The process of filling the apparatus with carbon dioxide, and of heating the contents of B, is repeated. When it becomes apparent, from the light color of the liquid in B, that all of the nitric oxide has been expelled from it, the current of carbon dioxide is increased and the heating discontinued. Care must be taken, however, not to admit too strong a current of carbon dioxide, lest some of the nitric oxide should be forced unabsorbed through the permanganate solution. It is also necessary, for the same reason, to avoid too rapid heating during the decomposition of the nitrate.

When all of the nitric oxide has been forced into the solution of permanganate, the determination is made in the manner already described.

To test the method, nine determinations were made with quantities of pure nitrate of potassium varying from 100 to 200 milligrammes. The maximum difference between the volumes of permanganate actually used and those calculated was 0.05 c.c., while the main difference was 0.036 c.c. The measurements of the permanganate were made from a burette which had been carefully calibrated. We also made a number of determinations, using a solution of manganous sulphate in the place of the oxalic acid. The advantage of this method lies in the fact that it is not necessary to dissolve the oxide which is precipitated upon the glass within the tubes, E, E, since, in the presence of an excess of permanganate, the reduction by nitric oxide extends only to the formation of MnO_{2}; also in the fact that the solution of manganous sulphate is more stable than that of oxalic acid. A solution of the sulphate having been once carefully standardized, can be used for a long time to determine the value of permanganate solutions.

The details of the method are as follows: A solution of manganous sulphate slightly stronger than No. 1 is prepared.

The difference between 100 c.c. of it and 100 c.c. of No. 1 is ascertained, according to the method of Volhard, by means of solution No. 3.

The contents of E, E, together with the rinsings from the tubes, are poured into a capacious flask. 100 c.c. of the manganous sulphate and a few drops of nitric acid are then added, and the whole boiled. Finally, the excess of manganous sulphate is determined, in the manner described by Volhard, by means of solution No. 3. Subtracting from the total amount of permanganate thus used the quantity required to equalize the 100 c.c. of solution No. 1 and the 100 c.c. of the manganous sulphate, we shall have the quantity of permanganate reduced by the nitric oxide.

It must, however, be remembered that the value of solution No. 3 is now to be calculated on the basis of the equation KMnO_{2} + NO = KNO_{3} + MnO_{2}. One molecule of permanganate equals one molecule of nitric oxide when manganous sulphate is used, since no part of the permanganate employed in this method is reduced below the superoxide condition. In other words, solution No. 3 now represents only three-fifths as much nitric acid as it does when oxalic acid is used.

The results obtained by this method were moderately satisfactory, but not quite so exact as those obtained when oxalic acid was used. A series of four determinations gave differences, between the volumes of permanganate calculated and used, of 0.05 to 0.15 c.c.

The principal objection to the method lies in the difficulty of determining, in the presence of the brown oxide of manganese, the exact point at which the oxidation is complete.

The carbon dioxide generator, A, was devised by us to take the place of the ordinary generators, in which marble is used. We have found that a submersion of twenty hours in boiling water does not suffice to completely remove the air which, as is well known, is contained in ordinary marble; hence some other substance must be employed as a source of the gas. In the apparatus which we are about to describe, the acid carbonate of sodium is used.

It consists of a long, narrow cylinder (450 x 60 mm.); a tightly fitting rubber stopper, through which three tubes pass, as shown in the figure; a small cylinder, F, containing mercury; and a sulphuric acid reservoir, G.

The tube, _g_, is drawn out to a fine point at the end and curved, so that the acid which is delivered into A falls upon and runs down the outside of the tube. The tube, h, dips under the mercury in F. G and _g_ are connected by means of a long piece of rubber tubing which is supplied with a screw pinch cock.

The apparatus is made to give any required pressure by raising or lowering G and F; but the elevation of G, as compared with that of F, should always be such that the gas will force its way through h rather than g. The upper part of the cylinder, F, is filled with cotton wool to prevent loss of mercury by spattering.

The material placed in A consists of a saturated solution of acid carbonate of sodium, to which an excess of the solid salt has been added. The sulphuric acid is the ordinary dilute. The apparatus, if properly regulated, serves its purpose very well. The principal precaution to be observed in using it is to avoid a too sudden relieving of the pressure, which would, of course, result in the introduction of an unnecessarily large quantity of sulphuric acid into A.

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WATER OF CRYSTALLIZATION.

By W.W.J. NICOL, M.A., D.Sc.

When a hydrated salt is dissolved, does it retain its water of crystallization, or does this latter cease to be distinguishable from the solvent water? Both views have found advocates among chemists who have looked at the question of solution, and both have been supported by arguments more or less to the point. But among the possible means of solving this question there is one which has entirely escaped the notice of those interested in the subject. And those who hold that water of crystallization exists in solution have been entirely oblivious of the fact that, while they are ready to accept the results of the modern science of thermo-chemistry, and to employ them to support their views on hydration, yet these very results, if correct, prove without a shadow of a doubt that water of crystallization does not exist in solution.

The proof is so clear and self-evident when once one's attention is directed to it, that, though I intend to develop it more fully on another occasion, I feel that it is better to publish an outline of it at once.

Thomsen has found that the heat of neutralization of the soluble bases of the alkalies and alkaline earths with sulphuric acid has a mean value of 31.150 c. within very narrow limits. When hydrochloric or nitric acid is employed, the value is 27.640 c., also within very narrow limits. Now, this agreement of the six bases in their behavior with sulphuric acid, much more of the seven bases with both HNO_{3} and HCl, is so close that it cannot be regarded as accidental, but, in the words of Meyer, the heat of formation of a salt in aqueous solution is a quantity made up of two parts, one a constant for the base, the other for the acid. But of the twenty salts thus formed, some are anhydrous in the solid state, others have water of crystallization, up to ten molecules in the case of Na_{2}SO_{4}. If water of crystallization exists in solution, it will be necessary to suppose that this agreement is accidental, which is absurd, as a glance at the probabilities will show. Thomsen himself expressly states that he regards the dissolved state as one in which the conditions are comparable for all substances; this would be impossible if water of crystallization were present.

A still stronger proof is afforded by the "_avidity_" of Thomsen or the "_affinity_" of Ostwald; both have worked on the subject, taking no account of water of crystallization, and the results, e.g., for H_{2}SO_{4} and HCl with NaHO, where water of crystallization _may_ come in, are entirely confirmed by Ostwald's results on inversion and etherification, where there can be no water of crystallization.

The proof is complete, water of crystallization cannot be attached to the salt in solution, or if it is, no heat is evolved on union more than with solvent water. The alternative is to suppose that the whole of the above thermo-chemical results are coincidences.

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ALPINE FLOWERS IN THE PYRENEES.

Bagneres De Luchon, in the department of the Haute Garonne, is a gay town of some 5,000 inhabitants. A friend told me that he once suffered so much from the heat there in June, that he determined never to go to the Pyrenees again. We were there the second week in June, and we suffered more from rain and cold, and were very glad of a fire in the evening.

Except to the south, in the direction of the Porte de Venasque, one of the chief mule passes into Spain during summer, where there are fine snow-capped mountains, the scenery from the town is not grand, but it is within easy reach of the wildest parts of the Pyrenees.

It is the nearest town to the Maladetta, their highest point, in which the Garonne rises, and among whose rocks is one of the last strongholds of the ibex or bouquetin, the "wild goat" mentioned by Homer. Eagles and vultures are to be seen sailing about the sky near Luchon nearly every day, and bears, which in the Pyrenees are neither mythical nor formidable, descend to within a few miles of the town after wild strawberries, which abound there.

We heard of two female peasants lately gathering wild strawberries who were suddenly confronted with competitors for the spoil in the shape of a she bear and two cubs. It was doubtful whether man or beast was the more surprised. The cubs began to growl, but their dam gave both of them a box on the ears for their bad manners, and led them away. As for flowers, the neighborhood of Luchon has the reputation, perhaps not undeserved, of being the most flowery part of the Pyrenees.

We went the usual expeditions from the town, in spite of the weather, and I will try to remember what plants we noticed in each of them. The first trip was to the Vallee du Lys. In spite of the spelling, the name suggests lilies of the valley, but we are told that lys is an old word meaning water, and that the valley took its name from the number of cataracts, not from lilies, there.

However this may be, a lily grows there in great profusion, and was just coming into flower toward the middle of June. It is the Lis de St. Bruno (Anthericum liliastrum), a plant worthy of giving its name to a valley of which it is a characteristic feature. Still more conspicuous at the time when we were there were the Narcissus poeticus, abundant all round Luchon, but already past in the low meadows near the town, but higher up, at an elevation of about 4,000 ft., it was quite at its best, and whitened the ground over many acres.

I looked about for varieties, but failed to detect any special character by which it could be referred to any of the varietal names given in catalogues, and concluded that it was N. poeticus pure and simple. Pulmonarias were abundant along the road, as also in the whole region of the Pyrenees, the character of the leaves varying greatly, some being spotless, some full of irregular white patches, others with well defined round spots. They varied, too, from broad heart-shaped to narrow lanceolate, and I soon concluded that it was hopeless to attempt any division of the class founded upon the leaves.

Besides the beautiful flowers of Scabious mentioned before, a new feature in the meadows here was the abundance of Astrantia major. A pure white Hesperis matronalis was also common, but I saw no purple forms of it. Geranium phæum also grew everywhere in the fields, the color of the flower varying a good deal. Hepaticas were not so common by the roadside here as at Eaux Bonnes, but are generally distributed. Many of them have their leaves beautifully marbled, and I selected and brought away a few of the best, in hopes that they may keep this character. I was struck everywhere by the one-crowned appearance of the Hepaticas, as if in their second year from seed.

On the mountains, where they were still in flower, I did not find the colors mixed, but on one mountain they would be all white, on another all blue. I do not recollect to have seen any pink. Meconopsis cambrica is common in the Pyrenees. I observe that in Grenier's "French Flora" the color of the flower is given as "jaune orange," but I never saw it either in England or in France with orange flowers till I saw it covering a bank by the side of the road to the Vallee du Lys. I was too much struck by it to delay securing a plant or two, which was lucky, for when we returned every flower had been gathered by some rival admirers.

Another expedition from Luchon is to the Lac d'Oo. This, too, is famous for flowers; but especially so is a high valley called Val d'Esquierry, 2,000 ft. or 3,000 ft. above the village d'Oo, at which the carriage road ends. Botanists call this the garden of the Pyrenees, and, of course, I was most anxious to see it.

The landlord of our hotel was quite enthusiastic in his description of the treat in store for me, enumerating a long catalogue of colors, and indicating with his hand, palm downward, the height from the ground at which I was to expect to see each color. I was afterward told that he had never been to the famous valley, being by no means addicted to climbing mountains.

During the first part of the drive from Luchon we saw hanging from the rocks by the roadside large masses of Saponaria ocymoides, varying much in the shade of color of the flowers. This is a plant which I find it better to grow from cuttings than from seed. The best shades of color are in this way preserved, and the plants are more flowery and less straggling. As we got near the end of the carriage road, the meadows became more crowded with flowers known in England only in gardens.

Besides such plants as Geranium pyrenaicum growing everywhere on the banks, the fields were full of a light purple geranium--I think sylvaticum. Here, too, I noticed Meconopsis cambrica with orange flowers. Narcissus poeticus was also there, and so were some splendid thistles, large and rich in color. But the most remarkable part of the coloring in the meadows was produced by different shades of Viola cornuta carpeting the ground. We noticed this plant in many parts of the Pyrenees, but here especially.

From the end of the road I started with a guide for the promised garden of the Val d'Esquierry. By the side of the steep and winding path I noticed Ramondia pyrenaica--the only place I saw it in the Luchon district. Other notable plants were a quantity of Anemone alpina of dwarf growth and very large flowers, covering a green knoll near a stream. A little beyond, Aster alpinus was in flower, of a bright color, which I can never get it to show in gardens. These, with the exception of a few saxifrages and daffodils of the variety muticus, were about the last flowers I saw there.

Promise of flowers there was in abundance. Aconites, I suppose napellus, and also that form of A. lycoctonum with the large leaves known as pyrenaicum, were just enough grown to recognize. The large white Asphodel, called by French botanists A. albus, but better known in gardens as A. ramosus, which grows everywhere in the Pyrenees, and the coarse shoots of Gentiana lutea were just showing.

Further on the daffodils were only just putting their noses through the yellow dead grass, which the snow had hardly left and was again beginning to whiten, for the rain, which had been coming down in torrents ever since I left the carriage and had wet me through, had now changed to snow. Still I went on, in spite of the bitter cold, hoping that I should come to some hyperborean region where the flowers would be all bright; but my guide at last undeceived me, and convinced me that we were far too early, so we went down again, wiser and sadder, and I advise my friends who wish to see the Val d'Esquierry in its beauty not to visit it before July at the earliest.

I have still one mountain walk to describe, a far more successful one, but it must be deferred till another week.--_C. Wolley Dod, in the Garden._

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Turtle shells may be softened by hot water, and if compressed in this state by screws in iron or brass moulds, may be bent into any shape, the moulds being then plunged into cold water.

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A CENTURY PLANT IN BLOOM.

A huge agave, or century plant, is now blooming at Auburn, N.Y. A few days ago the great plant became tinged with a delicate yellowish-white color, as its 4,000 buds began to develop into the full-blown flowers, whose penetrating fragrance, not unlike that of the pond lily, now attracts swarms of bees and other insects. The plant was purchased in 1837 by the owner, and was then twelve years old. For half a century the agave has lain around his greenhouses in company with several others, and no special care has been taken of it, except to protect it somehow in winter, that it might be fresh for the next summer's growth. The plant has always been a hardy specimen, and required little care. Its whole life, now speedily approaching a termination in the fulfillment of the end of its existence--flowering--has been a sluggish course. Its growth has been steady and its development gradual. Occasionally it has thrust out a spiked leaf until, in size, it became greater than its fellow plants and took on the likeness of an enormous cabbage which had been arrested in its development and failed to attain perfection. Early last April its appearance began to undergo a decided change. Its resemblance to a cabbage lessened, and it began to look like a giant asparagus plant. On April 12, the great fleshy leaves, massed together so as to impress the imprint of their spines upon one another, began to unfold, and a thick, succulent bud burst up amid the leaves. Slowly the stalk developed from the bud and assumed gigantic proportions. Green scales appeared in regular arrangement about the stalk, marking the points from which lateral branches were to spring. The thick stalk, tender and brittle at first as new asparagus, became tough and hard enough to resist a knife, and its surface assumed the gritty character of the leaves of the plant. The low roof of the hothouse became an obstruction to further growth, and had to be removed. Lateral limbs were, at a later period, thrust out in great numbers, each of them bearing small branches, as do strawberry plants, on which hang sprays of buds in bunches of from three to ten, making in all many hundreds, all waiting for the completion and blooming of the topmost buds. The inflorescence of the century plant is peculiar, and the appearance of flowers on the lower branches may be simultaneous with, or consecutive to, the blossoming on the upper limbs. With the appearance of the lateral outshoots the great aloe lost its likeness to asparagus, and at present bears resemblance to an immense candelabra. The plant is now fully matured, and has a height of twenty-seven feet. There are thirty-three branches on the main stem, and, by actual count, one of the lateral limbs was found to bear 273 perfect buds, some of whose green sepals have spread, revealing the yellowish-white petals and essential parts of the plant. The ample panicles crowded with curious blossoms are, as, indeed, the Greek name of the plant--agave--signifies, wonderful.

There is a pathetic view to be taken of the great plant's present condition. For years it has been preparing to flower, and the shoot it has sent up is the dying effort. The blossoms carry in them the life of new plants, and the old plant dies in giving them birth. It is commonly supposed that this plant, the _Agave Americana_, or American aloe, blooms only at the end of 100 years, hence the common name century plant.