SCIENCE. 



289 



essentially different curves representing heat and light 

 must be banished hereafter from text-books. The 

 old views on this subject can no longer be maintained 

 even by European men of science, who are prepossessed 

 in their favor. This result, fulfilling what was almost a 

 prophecy when made, a quarter of a century ago, by the 

 elder Draper, and, being due largely to means which 

 science owes to Mr. Rutherfurd, may, if obtained, be 

 most fairly claimed as largely due to the two Americans 

 whose names have just been cited. 



ON THE INTIMATE STRUCTURE OF CERTAIN 



MINERAL VEINS.* 



Prof. Benjamin Silliman. 



Ur. Sorby, of England, in his classical paper " On the 

 Cavities and Fluidal Inclusions found in Certain Varieties 

 of Quartz," made the sagacious suggestion that certain 

 fluidal inclusions observed by him in quartz consisted of 

 two fluids, viz., water and probably a liquified gas also. 

 An examination has recently been made of a remarkable 

 vein stone from a gold vein nown as " Hunter's Rest," 

 Arizona. This vein was capped by a black uncrystalline 

 rock resembling somewhat hornblend in a compact form. 

 But it was seen under the microscope with polarized 

 light to be compact tourmaline, a mineral never found 

 associated with gold. This black rock which is common 

 enough in connection with tin ore, is here abundantly 

 coated with gold. But beneath this black capping at a 

 very moderate depth, occurs the usual quartz billing of 

 gold-bearing veins — the quartz in this vein showing free 

 gold in brilliant points, and stains of copper green with 

 some pyrite, galena, etc. This quartz seen in thin sec- 

 tion under a high power, showed a multitude of fluidal 

 cavities, and among them were some which under a high 

 power {y% to 1-1 5-inch) showed distinctly two fluids, one 

 of which existed as an inner bubble, and which displayed 

 almost constant activity of motion. This second liquid 

 was liquified carbonic acid. Thin sections of the vein- 

 stone were placed upon a slide for examination. When 

 warmed, the carbonic acid expanded and the motion 

 ceased, bnt when permitted to become cold, it became 

 as active as before. Quartz with gold found in Southern 

 California near the Nevada line, is entirely destitute of 

 sulphurets, showing that the intervention of iron salts as 

 a solvent agent was not necessary in the formation of the 

 deposits of gold. 



THE TURQUOISE OF NEW MEXICO.* 



Prof. Benjamin Silliman. 



A number of domestic articles have recently been 

 found in excavations at Mount Chalchuitl, in Los 

 Cerillos, about twenty-two miles southwest of the 

 ancient town of Santa Fe. Among these are a 

 large stone hammer of the hard hornblendic Andalu- 

 site of which the mountains of the country are largely 

 formed ; a lamp, a pottery idol, such as are manufactured 

 to this day ; a spoon made of shell ; a perpect specimen 

 of a pottery dish, and some of the bones of the Pueblos or 

 Indian miners, who were killed in 1680 by the fall of a 

 large section of Mt. Chalchuitl, which had been under- 

 mined by them. These articles had been covered in the 

 caverns for 200 years when found. The rocks which 

 form Mt. Chalchuitl — the Indian name of the turquoise — 

 are distinguished from those of the surrounding and as- 

 sociated ranges of the Cerillos by their white color and 

 decomposed appearance, closely resembling tuff and 

 kaolin, andgi/ing evidence of an extensive and profound 

 alteration, due, probably, to the escape through them, at 

 this point, of heated vapor of water and perhaps of other 



* Read before the National Academy of Sciences, N. Y., 1880. 



vapors or gases, by the action of which the original crys- 

 talline structure of the mass has been completely decom- 

 posed or metamorphosed, with the production of new 

 chemical compounds. Among these the turquoise is the 

 most conspicuous and important. In the seams and 

 cavities of this yellowish-white and kaolin-like tuffaceous 

 rock the torquoise is found in thin veinlets and little balls 

 or concretions called " nuggets," covered on the exterior 

 with a crust of the nearly white tuff, and showing on 

 cross fracture the less valued varieties of the gem, more 

 rarely offering fine sky-b ue stones of higher value for 

 ornamental purposes. It is easy to see these blue stains 

 in every direction among these decomposed rocks, but the 

 turquoise in masses of any commercial value is extremely 

 rare, and many tons of the rock may be broken without 

 finding a single stone which a jeweller or virtuoso would 

 value as a gem. 



That considerable quantities of the turquoise were ob- 

 tained can hardly be questioned. The ancient Mexicans 

 attached great value to this ornamental stone, as the 

 Indians do to this day. The familiar tale of the gift of 

 large and costly turquoise by Montezuma to Cortez for 

 the Spanish crown, as narrated by Clavigero in his his- 

 tory of Mexico, shows the high value attached to this 

 gem. It is not known that any other locality in America 

 has furnished turquoise in any quantity. The origin of 

 the turquoise of Los Cerillos in view of late observations 

 is not doubtful. Chemically, it is a hydrous aluminum 

 phosphate. Its blue color is due to a variable quantity 

 of copper oxide derived from associated rocks. The 

 Cerillos turquoise contains 3.81 per cent, of this metal, 

 Neglecting this constituent the formula for turquoise re- 

 quires : phosphoric acid, 32.6; alumina, 47.0; water, 

 20.5. Total, 100. 1. Evidently the decomposition of the 

 feldspar of the trachyte has furnished the alumina, while 

 the phosphate of lime, which the microscope detects in 

 the thin sections of the Cerillos rocks, has furnished the 

 phosphoric acid. A little copper is diffused as a consti- 

 tuent also of the veins of this region, and hence the color 

 which the metal imparts. The inspection of thin sections 

 of turquoise by the microscope, with a high power, shows 

 the seemingly homogeneous mass of this compact and 

 non-crystalline mineral to consist of very minute scales, 

 nearly colorless, and having an aggregate polarization, 

 and showing a few particles of iron oxide. The rocks in 

 which the turquoise occurs are seen by the aid of the 

 microscope and polarized light in thin section to be plainly 

 only the ruins, as it were, of crystalline trachytes show- 

 ing remnants of feldspar crystals, decomposed in part into 

 a white kaolin-like substance, with mica, slag and glassy 

 grains, quartz, with large fluidal inclosures, looking like 

 a secondary product. There is a considerable diversity 

 in their looks, but they may all be classed as trachyte- 

 tuffs, and are doubtless merely the result of the crystal- 

 line rocks of the district along the line of volcanic fissures. 



ON A NEW GENERAL METHOD OF ANALYSIS* 



By Prof. Walcott Gibbs. 



The process consists essentially in passing a gal- 

 vanic current through the solution in such a man- 

 ner that a surface of metallic mercury forms the 

 cathode, and a plate of platinum the anode. Under 

 these circumstances the metal in the solution combines 

 with the mercury to form an amalgam. What is new in 

 this process is the fact that a number of metals, as for 

 example, iron, cobalt, nickel, zinc, cadmium, tin, mercurv, 

 etc., may be completely removed from the solution so that 

 the electro-negative constituent of the roll may be deter- 

 mined in the solution by ordinary methods, while the 

 metal itself is found by the increase in weight of the mer- 

 cury. The extent of the applications of the method and 

 its limitations remain to be determined. 



* Read before the National Academy of Sciences, N. Y,, 1^89, 



