GEOPHYSICAL LABORATORY. 163 



perature was tested by taking a series of measurements of the oxygen pressures 

 produced by 0.5-gram charges of iron oxide, heated at various levels in the 

 furnace. These indicate a length of about 25 to 30 mm., within which the 

 temperature is uniform within 1°. The furnace takes 580 amperes at 1.8 

 volts at 1450°, and can be held constant to 1° at this temperature. 



(10) Ein Vakuumofen fiir die INIessung kleiner Dissoziationsdrucken. R. B. Sosman und 



J. C. Hostetter. Z. Elektrochemie (in press). 



A German translation of "A vacuum furnace for the measurement of small 

 dissociation pressures" (J. Wash. Acad. Sci., 5, 277-285, 1915). Reviewed 

 under No. 9 above. 



(11) The reduction of iron oxides by platinum, with a note on the magnetic susceptibihty 



of iron-bearing platinum. R. B. Sosman and J. C. Hostetter. J. Wash. Acad. 

 Sci., 5, 293-303 (1915). 



Platinum acts on both hematite and magnetite at 1200° under low pressures 

 of oxygen, absorbing iron and giving off oxygen. It also reacts with mag- 

 netite in the same way at 1600° and at the usual atmospheric pressure of oxy- 

 gen. (Hematite is not stable in air at 1600°, but goes over into magnetite.) 

 On the other hand, it is well known to analysts that platinum crucibles in 

 which FejOs is ignited in air for weighing in analytical procedures take up no 

 such amounts of iron as were found to be absorbed under the conditions just 

 described. The reason for these differences of behavior is readily found in 

 the phase rule and the relations of iron and platinum in their alloys. The 

 results explain the very common occurrence of small amounts of iron in plati- 

 num, since platinum will exercise its reducing action on any material contain- 

 ing iron oxides with which it comes in contact, provided the temperature is 

 sufficiently high. At low temperatures, on the other hand, and with abundant 

 access of atmospheric oxygen, no appreciable reduction is to be expected. 

 The magnetic pull exerted by an electro-magnet on a sample of iron-bearing 

 platinum gives only a qualitative indication of the presence of iron, but no 

 quantitative measure of the amount present. 



(12) The calculation of calcium orthosilicate in the norm of igneous rocks. H. S. Washing- 



ton. J. Wash. Acad. Sci., 5, 345-350 (1915). 



In calculating the norm of igneous rocks according to the quantitative sys- 

 tem, the akermanite molecule, 4Ca0.3Si02, was used in certain cases. Recent 

 researches in the Geophysical Laboratory have shown that this molecule is 

 non-existent, that 3Ca0.2Si02 is unstable, but that 2CaO.Si02 is stable and 

 readily formed in melts low in Si02 and high in CaO. This molecule has 

 accordingly been adopted instead of 4Ca0.3Si02, and this paper presents the 

 appropriate new equations for its calculation, with examples, as well as a short 

 description of a modified procedure in calculating the norms of igneous rocks. 



(13) Contributions to Sardinian petrography, I. The rocks of Monte Ferru. H. S. Wash- 



ington. Am. J. Sci. (4), 39, 513-529 (1915). 



It is purposed to publish a number of analyses of Sardinian igneous rocks 

 which have been made in recent years upon material collected in 1905, begin- 

 ning with those of Monte Ferru, on the west coast of the island. 



The geology and structure of the volcano are briefly described. It is com- 

 posed of a huge central dome of trachytes, with subordinate phonolite, and 

 covered with a thick mantle of basalts. There are some small final flows of 

 analcite basalt. The main types are described petrographically, and eight 

 chemical analyses are given. 



