of lime. Such are the phosphates known as " West India phos""Bolivian guano, phate,' "" etc. These contain from 40 to 60 per cent. (and sometimes more) of ordinary phosphate of lime, whilst their per-centage of nitrogen (ammonia) dwindles down to 2, 1, or even 0.5 per cent., as the phosphate increases. Here, then, is an abundant source of phosphate of lime.

But several West India islands furnish a species of hard rock, of very peculiar aspect, consisting chiefly of phosphate of lime. Many persons consider that this rock has been derived from guano, supposing it to be the result of exposure to the atmosphere for thousands of years; others imagine it to be guano modified by volcanic action. I have examined this mineral phosphate,* and find that it contains not only phosphate of lime, but also a considerable proportion of phosphate of alumina a substance not met with in guano: it is, in fact, a compound of phosphate of lime and phosphate of alumina, containing about 17 per cent. of the latter, and 65 per cent. of the former. As this rock is principally derived from the little island of Sombrero, I called it Sombrerite. This is another tolerably abundant source of phosphate of lime, much used in the manufacture of superphosphate manure.

Another hard phosphatic rock, of a similar description, is found upon Monk Island, in the Gulf of Venezuela. Although I have received for analysis in my laboratory many hundred specimens of the different phosphates mentioned in this paper, I have never yet met with this one from Monk Island; but I have reason to believe it is a substance similar in all respects to Sombrerite. Whether it be so or not cannot be determined by the few incomplete analyses that appear to have been made of it hitherto. However, it constitutes a cheap source of phosphate to manufacturers of superphosphate manure; and it appears to contain 78 to 80 per cent. of phosphate of lime.

Another, and most abundant source of phosphate of lime is, I am happy to say, an indigenous one, and one which is very extensively utilized in the manufacture of superphosphate. I allude to the Cambridge and Suffolk coprolites. These are hard nodules, somewhat cylindrical, and having rounded edges. The Cambridge coprolites are found in the upper green sand, where they form extensive deposits, and are so intimately mixed, on their surface, with the green sand itself, that their true colour is only seen when they are broken. They contain 60 to 65 per cent. of phosphate of lime, sometimes rather more, and when ground form a yellowish-white powder. They are supposed to be the fossil excrement of extinct animals, hence their curious name, derived from the Greek; but we have not

*Journal of the Chemical Society, 1862.

sufficient proof of this extraordinary supposition. However, the revelations of geology during the past twenty years have been so exceedingly wonderful, that one is readily tempted to admit that some of these coprolites are the fossil excrement of certain extinct animals, probably reptiles, and therefore correspond somewhat in their chemical composition to guano which has been deprived of its organic matter by atmospheric influences. Specimens of such guano have given me, upon analysis, from 15 to 30 per cent. of carbonate of lime, which resembles the proportion of carbonate of lime invariably present in every description of coprolites.

The main thing that regards the agriculturist or manure manufacturer, however, is their chemical composition, by which these Cambridge coprolites appear to be the cheapest source of phosphate of lime at present known. The Suffolk coprolites are dark brown nodules, some of which have very much the appearance of fossil bones rounded by the action of the sea. They always contain a certain amount of red oxide of iron, and about 56 per cent. of phosphate of lime; they are consequently rather less valuable than the pure Cambridge coprolites; moreover, they appear to belong to the tertiary formations.

All these coprolites, and, indeed, all natural phosphates used in agriculture, except apatite (see further), contain a certain amount of carbonate of lime and insoluble silicious matter, and it is important to manufacturers and agriculturists to have the proportions of these determined accurately, otherwise they have no control over adulteration, and no basis to work upon in the manufacture of artificial manures.

Along with Cambridge coprolites I have found fragments of fossil bone-bones of reptiles, probably-showing the same chemical composition as the rounded nodules or coprolites themselves. The Suffolk coprolites appear to be chiefly fossil bone, more or less impregnated with phosphate of iron, etc.

But the whole of the Upper Green Sand formation of England is characterized by a wide diffusion of phosphoric acid in the shape of phosphate of lime. My attention was called to this some years ago, by a relation who forwarded to me a very large specimen of fossil wood from the Green Sand of the Isle of Wight, which, upon being submitted to analysis, gave me an enormous proportion of phosphate of lime-in fact, it was chiefly formed of this substance and fluorspar-though it was not apatite; and I learnt afterwards that Mr. Thomas Way had formerly examined several fossil polyps, sponges, etc., from the Green Sand, which gave a very large per-centage of phosphate of lime.

*See Report of British Association, 1861, and Chemical News, 1861.

This proves to us that a great amount of phosphates has been diffused through the Upper Green Sand formations, may-be by the accumulated excrement of myriads of fish and large reptiles which inhabited this country at the remote geological periods to which these formations belong.

I have since analyzed many other sedimentary rocks and fossils, in order to discover whether they contained any notable quantity of phosphate of lime, but rarely found more than one or two per cent., frequently a mere trace only. However, there exist, doubtless, other sources of phosphate yet to be discovered.

If we admit that the mineral phosphate Sombrerite and that of Monk Island be similar minerals, and have been derived, by some unknown geological process, from guano; if we admit, moreover, that the coprolites found in Cambridge and Suffolk are, like those of the Coal and Lias formations, true fossil excrements, mixed here and there with bone; and, thirdly, if we admit that the other numerous and above-named fossils (wood, sponges, polyps, etc.) fossilized by phosphate of lime, be the result of an impregnation of organic substances by the excrementitious matter of animals now extinct, what a splendid example we have here of applied paleontology. For since agricultural chemistry began its rapid development, all these "fossil excrements" have become valuable as a means of aiding us to keep up the fertility of our soils, to increase our wheat crops, and to have an abundant and cheap supply of bread. We are thus tempted to class all phosphates used in agriculture, including bones, bone-ash, etc., as derived from organized beings that have once flourished upon our globe.

But we have another source of phosphate of lime in the coarse variety of apatite of Estremadura, which appears to have had no connection with organized beings of any description, and cannot be considered as a fossil. The Estremadura phosphate met with in commerce is the mineral apatite in the massive form; it is abundant in Spain, and may be in other countries also, but up to the present time it does not appear to be so plentiful as the other phosphates mentioned in this paper. However, it is of all known substances found in nature that which contains the most phosphate of lime, the per-centage of which in the commercial specimens averages from 85 to 87 per cent., and in absolutely pure specimens as much as 92.

The remaining phosphates used in agriculture are bones, bone-ash, and animal charcoal. The two latter are merely burnt bone. Bones contain the peculiar phosphate known as "boneearth," equivalent to about 56 per cent. of ordinary tribasic phosphate of lime. When ground, they often become mixed with silica and other impurities. Enormous cargoes of ox

bone, either sun-dried or in the shape of bone-ash, are imported from South America into England.

Bone-ash is bone burnt in contact with the air until its organic matter is destroyed; it yields a quantity of bone phosphate equivalent to 70 or 90 per cent. of ordinary phosphate of lime, according to its degree of purity. When burnt without contact of air, animal charcoal is obtained; this is used to clarify sugar, juice, etc., and when spent is burnt over again. After being thus burnt twice or thrice, it becomes comparatively useless to the sugar-refiners, and is sold to manufacturers of superphosphate. According to a number of analysis made of this substance in my laboratory, it may be said to average from 70 to 80 per cent. of phosphate of lime.

Such, then, are the substances which furnish our agriculturists, our lucifer-match manufacturers, our colour-makers, etc., with their supplies of phosphate of lime. It is needless, perhaps, to add that agriculture absorbs by far the greatest portion of this phosphate, and we may be thankful that there exists so plentiful a supply of it. In a future paper I will consider our present sources of ammonia.

SNOW CRYSTALS.

BY E. J. LOWE, ESQ., F.R.A.S., ETC.

WHEN we observe the snow beating against our windows, or being drifted into heaps by the wind, we regard it with interest, we admire its dazzling whiteness, and we are thankful to look upon its carpet, because it is a protection to tender plants from the injuries of severe frost. Few of us, however, are aware of the exquisite beauty of some of these snow crystals; very various in form, and sometimes exceedingly intricate, it becomes impossible to do justice to a snow-storm. The difficulties to be overcome are great: a lovely star descends and alights upon a leaf; paper and pencil are at hand, and the magnifying-glass reveals its beauties, but before it can be sketched in all probability it has melted and gone. If snow falls in showers, and the temperature of the air is above the freezingpoint, it is almost impossible to sketch the crystals. Once or twice a year the weather is sometimes favourable for these investigations, and such a day was February 10, 1864. Let us take this day as an example :

There had been a severe frost, the temperature falling to 15.8° at the height of four feet, and to 13-1° on the grass. The morning was overcast, foggy, dark, and having a peculiar yellow

smoky appearance, that is not uncommon on the advent of snow. At 9h. 15m. A.M. few snow crystals commenced falling; at 10h. 30m. A.M. the temperature at four feet was 25.8°, wet bulb thermometer 25-3°; on the grass, 24-7°; whilst, if we turn to the internal temperature, we shall observe that below the surface

At two inches on drained land it was

دو

25.8°

22.3°

20.8°

At four
At six
At two inches on undrained land it was 22.8°

The ground and air were, therefore, in such a condition that the snow would not melt. At first the snow crystals were solid, opaque, rounded, and confused in the interior, yet exhibiting the usual six-sided or hexagonal form. Amongst these crystals Fig. 1 a was detected, resembling six small feathers fastened together, and presently another, Fig. 1 8, not unlike an arrangement of fern fronds, having a central opaque star. From this time (10h. 15m. A.M.) the crystals were most beautiful. A third, somewhat similar to the last-mentioned, yet having the branches transparent and six-sided; then came a solid flat lozenge.

The next crystal is more especially worth notice, as it was changed artificially. It is represented in Fig. 2 a, fern-like at the tips, but feathered within in the manner of a fir branch, quite opaque and snowy white; on breathing gently on this crystal it partially melted, and froze again as a colourless transparent six-rayed star, Fig. 2 B, quite simple in its construction.

Fig. 1 represents another star with spinose edges; there was also a crystal somewhat similar, in the form of a cuneate wheel, solid and opaque.

Fig. 2 y was a leafy star, then came quite a different crystal from all the others, naked in its branches, but instead of being flat, it took the form of a ball.