1st. Two samples of aurifercus earth taken from the surface of the ground, in two parts of the Valley of Sacramento. 2nd. Auriferous sand, resulting from very thoroughly washing the same earth, and in which bractes of gold are distinctly visible. 3rd. Pieces of quartz and fragments of rocks collected in the alluvion which constitutes this valley. 4th. Two pieces of native gold. 5th. Lastly, bracteæ of gold from three different parts of the Sacramento, namely, from the American river at its entrance into the Valley of Sacramento; from the same river at 48 kilometres (about 30 miles) from its mouth; and from the River de las Plumas, from 60 to 72 kilometres (37 to 45 miles) distant from the first. These three points make known nearly one-fifth of the valley of Sacramento, which commences in the Sierra Nevada (Snow Mountains), and terminates in the ocean at the Port of San Francisco. Its course, which is nearly east and west, is from 336 to 360 kilometres long (210 to. 225 miles). The bractes of gold from California are much larger than those of the washings of the Oural and Brazil. They likewise differ from them in their reddish color, which enables us to distinguish them at first sight; their composition, according to the analysis made by M. Bivot, is Gold Silver.... 90.70 8.80 The earths of the Valley of Sacramento are light; to the touch they are very soft, but rubbing on the hand discovers some rough particles: their color is a light brown; the microscope shows them to be almost entirely silicious; the small fragments of which they are composed are angular and transparent; they very readily collect in lumps, and resemble, in color and transparency, a saline mass: by the naked eye only very few distinct grains are visible. The piece of gold sent to the Ecole des Mines, weighs 47.9414gr. (about 740gr.); its color is reddish; its composition is very analogous to that of the gold in bracteæ. This piece adheres to milky white quartz, whose surface resembled that of pebbles, washed in a river; however, it retains its general form, which is that of a thick, flat, and irregular vein. The general color of these sands is black. It is perceived at the first glance that oxide of iron predominates in them, and that it is to that mineral that their color is owing. I therefore commenced by separating the oxide of iron by means of the magnet: 3 grammes gave 1·79gr. of oxide of iron, or 59.82 per cent. Notwithstanding the separation of this large proportion of oxide of iron, the sands retained their black color: they were very rich in gold, and a greater number of bractea were observed in them. Examined with the microscope, the sands remaining after the separation of the oxide of iron contained some octohedral crystals, some with reflecting and but little altered faces-others rounded, but still brilliant. These crystals, from their form, and the color of their dust, appeared to be the titaniferous oxide of iron. They were mixed with flattened crystals, which, from their hexahedral projection and red dust, may be regarded as specular iron ore. Finally, among the black grains were observed very tender, dull, irregular fragments, which had all the characters of manganese. The titaniferous oxide of iron predominated greatly in this second portion of the sands, the manganese, on the contrary, being much more rare: this second kind of oxide of iron was clearly distinguished from that separated by means of the magnet: the latter, fragmentary and tarnished, is rounded in some parts. Mixed with the titaniferous oxide of iron, in the second portion of the sands of California, were found many white crystals of zircon, terminated at their two extremities, whose forms are very clear. These are1. Four-sided prisms, surmounted by an octohedron with a four-sided base, placed on the angles. 2. This same prism, presenting, besides the octohedral points, facettes, i, resulting from the intersection of the common angle in this octohedron and the prism. 3. Prisins with eight faces formed by the two four-sided prisms M and h'. These crystals are generally very short. Their perfect transparency, with their total absence *Annales des Mines, tome xiv., p. 105; of color, caused them to be taken, at first sight, for quartz; but, on counting the The form of this piece and the presence of quartz show us that, in its primitive situation, the gold forms veinules with a quartzy gangue. 1848. number of their faces, which it is very easy to do with some of them, it cannot be doubted that they belong to a prism with a four-sided base. Notwithstanding their small dimensions, the clearness of these crystals is so perfect, that the incidence of several of the faces may be measured. M. Descloizeaux found that the angle of i on i is 147° 30′, which differs only a few minutes from the value of the corresponding angle in the zircon. I was also able to observe the angle of the faces i on i and M on i in crystals of zircon from New Granada, of which I shall speak further on. I obtained for their values 133° and 149°, which approximate to the values 133° and 148° 7′ given by Philips for the same angles. A remark which appeared to me interesting, at least in the point of view of the power of crystallisation, is that the crystals of zircon are often penetrated with other crystals which are entirely enclosed in it, as observed with the needles of titanium in rock crystal. These crystals, often of a milky white, or even colorless, are perfectly distinguished under the microscope by the different manner in which light falls on them; some are of a hyacinth red. The white zircon, so abundant in the sands of California, is generally rough. I remember that it exists in some abundance in the Zillerthal, in the Tyrol. The sands of California contain also colorless hyaline quartz and smoky hyaline quartz. This quartz, always fragmentary, is distinguished by its vitreous and conchoidal fracture; there are, indeed, remarked in it fragments of a light blue, which can only be corindon. The grains of washed sand are generally Om. 00005 in length, and 0·00001 in diameter; these dimensions admit of their being isolated, or, at least, easily grouped under the microscope. I profited by this circumstance to establish approximatively the proportion of the elements which I have just noticed; it was sufficient for me to calculate them. In the first operation I operated on only 560 gr., in the second, on 352; the mean of these two operations gave the following results :Oxide of Iron obtained by the magnet 59.82 Titaniferous oxide of iron, specular iron, with a trace of oxide of man 16.32 The difference which exists in the size and form of the grains, and that presented by the specific gravity of each of the elements of which the auriferous sands of California are composed, should cause these proportions to be considered as giving only a rough approximation to their composition. However, they correspond very well with the idea of its composition formed on looking at it, and are interesting from the indications which they furnish of the nature of the auriferous soil. It will be remarked, besides, that the specific gravity of the sands of California is about 4.37, and that the oxide of iron weighs 5:09. These numbers agree very well with the composition above indicated. The crystalline state of the titaniferous oxide of iron and of the zircons show that the ancient soils whose destruction has produced the auriferous alluvion of the Valley of the Sacramento are not distant, and everything leads me to consider it as belonging to the chain of the Sierra Nevada. The perfect preservation of these crystals, and especially the particular circumstance of being terminated at their two extremities, makes me conjecture that these rocks are schistous. In the granites, indeed, the crystals adhere to the rock, and present only one summit; in schistous rocks, on the contrary, the crystals, very frequently lying in the direction of the stratification, are complete. Such are the staurotides and the disthenes of Saint Gothard, disseminated in_the_talcky schist, the macles of Coray in Brittany, and especially the small crystals of tourmaline so frequently met with in the micaceous schists of Morbihan. There is, therefore, reason to believe that the Sierra Nevada, or Snowy Mountains, which form the western limit of California, are, in great part, micaceous schist and talcky schist. The interest I felt in the examination of the auriferous sands of California made me desire to compare them with the auriferous sands of several localities, and I have made a comparative study of the auriferous sands of New Granada, sent to me by M. Amedée Burat, and of the sands of the Oural, detailed by M. Le Play. SANDS OF NEW GRANADA. The sands of New Granada were collected 9-10 in the Valley of Rio Dulce, situated in the 13.70 province of Antroquia; they are almost 0.67 entirely crystalline, like those of California. 0-29 The forms of the crystals of titaniferous oxide of iron and zircon, are even in a better state of preservation. These sands are rather gray than black; also the magnet gave me from 6gr. 70 of sand, only 2gr. 30 of oxide 100.00 * The gold was determined by the dry assay. of iron, or 34.35 per cent.: there remained, after this first operation, a sand composed of titaniferous oxide of iron, specular iron, zircon, and quartz. The first two minerals, although very abundant, are not nearly so plentiful as in the Californian sand. I have not here counted the grains, the smallness of many of them having rendered this operation difficult. I simply estimated them by sight, separating from them as much as possible, under the microscope, the grains of a different nature. According to this estimation they were composed of Magnetic oxide of iron obtained exactly ... ...... Titaniferous oxide of iron and specu 34.35 Among the crystals of titaniferous oxide of iron and specular iron, a certain number have preserved easily appreciable forms. They have, in general, much lustre: the crystals of zircon, for the most part very clear, are frequently terminated at their two extremities; they possess the red orange color proper to that mineral. These crystals are longer than those of California; their forms, although the same, differ, however, essentially in the difference of the extension of the faces. These are four-sided prisms, h', surmounted by a long dioctohedron, and terminated by very short facettes, a'. They are perceived only in the projection of the crystals, by an obtuse point which terminates them. The quartz, almost always fragmentary, is little rounded; some crystals are even observed in it terminated at their two extremities. It may be said in general that the auriferous sand of New Granada is less rounded than that of California, from which it may be presumed that it comes from a less distance. In fact, in comparing the distance of the Andes from the Valley of Rio Dulce, we find it to be only 80 kilometres (about 50 miles), whilst we have seen that the Valley of the Sacramento was nearly 400 kilometres (about 250 miles) long. The sands of New Granada are less rich in oxide of iron than those of California, which might be owing to their washing not having been pushed quite so far; these are the only differences which have been observed; their composition is, on the contrary, identical. From this it may be concluded that the mountains which have produced them by their denudation, are of the same nature, and that the Andes, for a length of more than 4,800 kilometres, present a complete identity. The regularity of this chain, which forms every where the barrier of the great ocean, naturally gave this idea; but the proof of the material fact is not the less interesting, and the study of the sand shows us their identity, even in all the details, which geology is not always in a condition to observe, for the minerals which they contain are disseminated in an inappreciable manner in the rock, whilst the diluvial phenomena which have at once isolated them from the rock, and concentrated in the earth, offer an easy means of studying them. (To be concluded in our next.) OBSERVATIONS ON THE USE OF THE SESQUIBASIC PHOSPHATE OF SILVER IN MINERAL ANALYSIS, AND IN ORGANIC ANALYSIS FOR THE DECOMPOSITION OF THE ALKALINE AND EARTHY CHLORIDES.* BY M. J. L. LASSAIGNE. WE owe to Chenevix the use of sesquibasic phosphate of silver for separating chloride of barium from chlorate of baryta, in the preparation of the latter salt. It was by this process, now almost abandoned, that this salt was first obtained in the laboratories in a pure state, so that its principal qualities could be studied. The decomposing action exercised by hydrated sesquibasic phosphate of silver on alkaline and earthy chlorides induced us to try this metallic salt-1st, for isolating certain nitrates of the alkaline and earthy chlorides; 2nd, for separating the saccharine principles mixed with chloride of sodium, as met with in certain organic products. The first means were employed by us in an analysis of water from a well. It is known that the salts soluble in concentrated alcohol consist principally of chlorides of magnesium and calcium, frequently associated in a greater or less degree with nitrates. Being desirous of ascertaining the proportions of nitrate of magnesia and chloride of magnesium in a mixture obtained with alcohol from the residue of some water from a well near Paris, we tried the use of hydrated phosphate of silver on a solution of these two salts. We soon found that, by the application of a gentle heat, the chloride of magnesium was completely converted into *Comptes Rendus, No. 7, Aug. 13, 1849. chloride of silver and sub-phosphate of magnesia, insoluble in water; whilst the nitrate remained in solution and was obtained by the evaporation of the solution. This simple method may be used in a great many circumstances: it succeeds equally well with a mixture of nitrate of lime and chloride of calcium, as we have distinctly proved. A small quantity of phosphate of silver remains dissolved in the water with the alkaline nitrate; but it is very trifling, and is easily allowed for in a quantitative analysis. The separation of an earthy nitrate from a chloride can be well effected only by evaporating to dryness the solution, in which must be an excess of hydrated phosphate of silver, and treating the residue with cold distilled water, so as to remove the insoluble products by filtration. It was by operating thus that we were enabled to estimate precisely the small quantity of nitrate of magnesia which was mixed with chloride of magnesium in the residue of some water from a well. We think that this process may be used with advantage to perform analogous separations in the analysis of mineral waters. We have made another application of this same phosphate of silver in the separation of cane and grape sugars, mixed with a small quantity of chloride of sodium. These two substances, soluble in alcohol, are sometimes met with mixed in certain organic products. The action of the phosphate of silver on a solution of such a mixture, forms, at the ordinary temperature, insoluble chloride of silver, and soluble phosphate of soda, which remains mixed with the sugar. Now, the phosphate of soda being insoluble in alcohol at 88 degrees, whilst sugar, on the contrary, is soluble in it, the possibility of effecting a separation by acting with alcohol on the product evaporated to dryness, is evident. Direct experiments have convinced us that cane and grape sugars, thus separated, retained merely a trace of the chloride of sodium which had been purposely mixed with them. In acting without heat and promptly on easily soluble principles, to separate the chlorides they may contain, there is no reason to fear the reducing action of the organic matter on a portion of phosphate of silver. ESTIMATION OF CARBONIC ACID IN MINERAL WATERS.* It is not without some difficulty that chemists called upon to analyse the water of a gaseous spring are able to ascertain exactly * Journal de Chimie Médicale, Sept., 1849. the volume of carbonic acid gas contained in it. This estimation cannot be made with accuracy in the laboratory; indeed, it is necessary to know the volume of gas contained in the water of the spring itself, and not that which may be left in the same water after having remained for any time in bottles. Whatever precautions may be used to prevent escape-however rapidly the vessels may be filled-whatever care we may take in the selection of stoppers, sealing the bottles, &c., we always find, in an analysis made in the laboratory, less gas than in one made at the spring. The means ordinarily employed are the mercurial bell-glass receiver, or boiling under the bell-glass, processes whose actual accuracy we do not dispute; but if we consider the inconveniences already noticed, and add the further loss of gas during the opening of the bottle and the pouring of the liquid into vessels for the experiments, it must be admitted that the quantity found will be merely a few fractions, and that it will be impossible to ascertain the exact amount of gas contained in the spring water. On the other hand, it is impossible, at least in the majority of cases, to convey to the spring the apparatus indispensable for making on the spot the necessary experiments. Mercurial troughs, especially, may be regarded a immoveable; besides, they are not in all laboratories, nor within the reach of practitioners of small localities. This removal would occasion in all cases some expense. A much more simple process, as easy, more convenient, and within the reach of every one, may, it appears to me, be employed with success. Before proceeding to estimate the carbonic acid gas, it is necessary to prepare, in a large vessel--a boiler for instance-a sufficient quantity of lime water. The lime must be quite fresh, and the water must be filtered. It may be poured into bottles, which must be perfectly fitted and corked immediately. After having done this, one or two quarts of the lime water are poured into a suitable vessel of sufficient capacity, and immediately after one quart of the gaseous water just taken from the well. It is useful to receive the mineral water into a measure capable of containing exactly a quart, and not into a bottle, in order that the water may undergo as little agitation as possible during the mixing of the two liquids. This mixture is continued alternately for several quarts, and the action of the gas on the carbonate of lime obtained is verified. If the quantity of gas contained in the mineral water is consider able, the excess of gas re-dissolves the car bonate of lime precipitated. In this case, a superabundance of lime may be added to effect the absorption of all the free gas contained in the mineral water. If the precipitate is abundant, the alternate addition of lime water and mineral water is continued until the latter amounts to 10 quarts. After the mixing has been well effected, and the combination of the carbonic acid has taken place, the precipitate obtained is allowed to subside, and more lime water is added to ascertain that all the gas is saturated. If by this addition a further precipitate be formed, more lime water must be added, until it exists in excess and occasions no further precipitate. This being ascertained, the liquid is left to settle for a short time, and when the precipitate is deposited all the water is decanted, as far as possible, carefully avoiding any waste of the carbonate produced. The precipitate is collected in a filter whose weight has been noted. As soon as the water has perfectly drained off, the product is washed on the filter with pure water (not gaseous) in order to remove the excess of lime water, which, becoming saturated by the gas contained in the atmospheric air, would interfere with the accurate appreciation of the carbonate of lime obtained by acting, as above, on the spring water. The precipitate contained in the filter is perfectly dried, after which it is weighed, and the weight is noted, the tare of the filter being deducted. In this operation the lime dissolved in the water combines with the carbonic acid gas, producing insoluble carbonate of lime. This carbonate precipitates, but not alone: the mineral water, deprived of one of its constituent principles, deposits at the same time the other insoluble carbonates, lime, magnesia, and iron. It retains only the soluble salts, which are removed by decantation and washing. water, and from this precipitate it will be easy, by means of a simple rule of proportion, to ascertain the volume of gas contained in the precipitate obtained, or, in other words, in 10 quarts of gaseous water. Five grammes of carbonate of lime being equivalent to 1 litre and 21 centilitres of carbonic acid gas, the whole may be easily appreciated. Example:Grammes. Precipitate obtained from 10 litres (quarts) of gaseous water, with sufficient lime water to completely saturate it... Deduct the carbonate of lime produced by the normal salts contained in the gaseous water Remaining.. ...... 28 75 2.25 26.50 5 1 lit. 21:: 26.50 : x=61. 313. The 10 litres, therefore, contain 6.313 lit. of free gas, or 0·6313 per litre. When the object is limited to ascertaining the quantity of carbonic acid contained in the mineral water, the operation is very much simplified: it is then sufficient to boil for a short time 10 litres of the same water. The disengagement of the gas effected during the boiling precipitates the insoluble carbonates held in solution. The latter are collected on a filter previously tared, then they are dried and weighed. The product of the filtration is evaporated to dryness, and the quantity of bicarbonate of soda or potassa originally held in solution in the water is appreciated; from these results we determine by calculation the carbonate that this salt produced with the lime water; this product is added to the carbonates deposited during the ebullition of the water, and subtracted like those of the first precipitate. Example: Grammes. Precipitate obtained from 10 litres of gaseous water, with sufficient lime water to completely saturate.... Deposit produced by boiling..2.50 Carbonate produced by the carbonate of soda or potassa..... Remainder.. 24.25 3.25 0.75 21.0 5: 121 :: 21 : x=5·8. Ten quarts contained, therefore, 5.8 litres of free gas. This first operation being completed, the analysis of the other substances, besides carbonic acid contained in the mineral water, is continued according to the ordinary methods, subtracting from the known weight of the lime precipitated that of the insoluble carbonates. If the mineral water contains, as is most frequently the case, bicarbonate of soda or potassa, these salts also augment the produce of carbonate of lime precipi- ON A CHROMATE OF COPPER AND tated. These alkalies abandon their carbonic acid gas and become caustic. It is necessary, therefore, to take account of their action on lime water, and to deduct, by calculation, the carbonate produced. These subtractions being made, there will remain only the carbonate of lime produced by the free carbonic acid of the mineral POTASSA.* BY A. KNOPP. THIS salt forms a pure light-brown powder, iridescent in the sunshine, consisting of transparent microscopic six-sided plates. It is * Annalen der Chemie und Pharmacie, April, 1849. |