342 



KNOW Li:i)(iE. 



Si;i"Ti;miii;k. 1<>i; 



tests, ti)o, with iiiixt lilies cuiilaiiiini;; inaiigaiicso dioxide, red 

 load and lead peroxide, tlie same volatile coiiipnund was also 

 obtained at low Icinperatures (about 50°C.). It would, there- 

 fore, appear that to prevent the formation of the poisonous 

 volatile substance, the pigments used with the linseed oil 

 should contain neither a hydrated compound such as white 

 lead nor an oxidisiu); agent such as red lead. Driers acting 

 by oxidation, such as manganese driers, are also objection.able 

 for the same reason. 



By raising the tempcratnn' to about ')0C. the poisonous 

 substance was also emitted by pastes containing silica. Ic.id 

 sulphate and zinc white, but llie absorption band in the 

 spectrum did not appear at lower temperatures. The relative 

 ease with which the pigments produced the volatile product 

 could be expressed in the following ratios : — /^inc white or 

 basic lead sulphate, ten ; white lead, one hundred and fifty ; 

 and lead hydroxide, two hundred and fifty. 



The general conclusion was tliat the poisonous compound 

 was given off by any paint containing an oxidising agent, and 

 that the symptoms experienced by people living in a freshly- 

 painted house must be attributed to this substance and not to 

 specific lead poisoning. 



.Apparently it consists of an unsaturated aldehydic com- 

 pound formed from the oil, and the means of preventing its 

 formation are to replace wliite lead in the paint by basic lead 

 sulphate or zinc white, and to have as little driers as possible 

 in the mixture. 



l'Ki:i\\K.\TION OF NITRATES FROM TIIK 

 ATM0S1'II1:RK.— Mr. E. K. Scott, writing in the Joiini. 

 Koy. Soc. Arts. (1912, LX, 645). gives an outline of the 

 present state of the industry of obtaining nitrogen from the 

 air. With refere?ice to the Birkeland-Eyde process, it is 

 mentioned that the factories now possess installations of two 

 hundred thousand horse power, which will be increased by 

 fifty per cent, during the next four years. The towers em- 

 ployed to absorb the nitrogen peroxide produced have been 

 very greatly reduced in size by the use of special pacUing 

 material of earthenware instead of quartz fragments. The 

 installations now at work or in process of building are 

 capable of producing over two hundred and fifty thousand tons 

 of calcium cyanamide (nitrolim) per year. The development 

 of the industry in this country is checked by the want of a 

 cheap source of electricity for the working process. 



GI'.OLCX.V. 



Hy G. \V. TVKKKI.I.. A.K.C.Sc, F.G.S. 



THE ALKALINE IGNIXJUS ROCKS OF AVRSHIKi:. 

 — Recent researches by the writer have shewn that the 

 intrusive igneous rocks of the Ayrshire Carboniferous, 

 hitherto designated simply as " dolerites " on the geological 

 maps, include a rich variety of pctrographic types, some of 

 which are new {Geological Magazine, February-March, 

 1912). They form a homogeneous suite which can be shewn 

 to be connected with a volcanic episode at the close of the 

 Carboniferous period, the remains of which form a small 

 basin-shaped are.i of lavas in the district about Mauclilim- 

 and Tarbolton. 



The rocks of this petrographic province are, in general, of 

 basic character, and are rich in alk.ilies and combined water. 

 The retention of water in an alkali-rich magma has resulted 

 in the rocks of the suite being characterised by analcite, a 

 mineral whose claim to be regarded as an original constituent 

 of igneous rocks has not long been admitted by the majority 

 of petrologists. Many of the other minerals are also rich in 

 alkalies. Soda-pyro.\enes and amphiboles and nepheline are 

 abundant in some of the rocks. 



The intrusive rocks occur as stratiform sills, small lenticular 

 masses, and as plugs and irregular intrusions in volcanic 

 necks. Petrographically, they are classified as follows: — 



A. — Rocks with conspicuous analcite. 



B. — Rocks with conspicuous nepheline. 



C. — Rocks without conspicuous analcite or nepheline, but 

 which may contain either as an accessory constituent. 



The most abund.int rocks of the first group, and of the 

 whole suite, are the tcsclictiitcn, gabbro-like rocks character- 

 ised by abundant analcite. Occasionally these assume ultra- 

 basic modifications, and arc to be described as/)icn7c. Some 

 of the picrite-leschenite masses shew the most extraordinary 

 ditTerentiation, many distinct types being found in the same 

 igneous unit. Some of the analcite rocks are new to science, 

 notably one called liigarile, from its type-locality of Lugar. 

 This rock contains nearly fifty per cent, of analcite and 

 ncphcline.thc remaining half beingcumposed of soda-pyroxenes, 

 .imphiboles, ilmenite, labradorite and apatite. Another rare 

 variety is analcitc-syenitc, characterised by the combination 

 of analcite with alkali-felspar, and strictly analogous with the 

 nepheline and leucite syenites. This rock is remarkable for its 

 extreme freshness and for the abundance of aegirine, a soda- 

 pyroxene rare in Scotland. .\ monchiquite, with huge pheno- 

 crysts of hornblende and biotite, completes the analcite-bearing 

 suite, and has been described at length in a former note 

 (" Knovvledgu," Vol. XXXIV, page 405). The nepheline- 

 bearing rocks include cssexitc. theralite. hitherto unknown 

 in Britain and remarkably fresh, and kylitc, a new type 

 which may be characterised as an olivine-rich, ultrafemic 

 theralite or essexite, and so named from its abundance in the 

 Kyle district of .Ayrshire. 



The rocks belonging to the third group may be called aifca/i- 

 dolcrites. They include numerous and varied doleritic types, 

 characterised by purple soda-bearing pyroxene and accessory 

 analcite or nepheline. 



The lavas of the Mauchline basin consist mainly of very 

 basic olivine-basalts, but certain of the types contain a good 

 deal of original analcite, and may be designated analcite- 

 basanite. Others contain fresh nepheline, and are true 

 neplieiinc basalts. Recently, nepheline basalts fully as fresh 

 and jjerfect as any of the Continental Tertiary examples have 

 been found in the river Ayr, near Mauchline. 



These rocks form a petrographic province whose boundaries 

 are approximately those of the county of Ayr, although some 

 part of it may be faulted down beneath the F'irth of Clyde. 



THE SEARCH FOR POTASH IN THE CNITED 

 STATES. — Practically all the potash salts of mineral origin 

 consumed in American industries are imported from Germany, 

 whicli is the only country where potash mines arc profitably 

 worked. .As the potash salts imported into the United States 

 in 1910 cost nearly twelve million dollars, and this amount 

 may be expected to increase rapidly in the future, the alert 

 and eflicient Geological Survey of that country set itself to 

 discover whether the United States could not supply, at least 

 partly, the needful potash, and thus break down the German 

 monopoly which results in enhanced prices. 



.Among the available sources of mineral potash arc the 

 potash-rich igneous rocks which contain minerals such as 

 leucite and orthoclase. The largest area of leucite-bearing 

 rocks in the United States embraces the Leucite Hills of 

 Sweetwater County, Wyoming. These have been investi- 

 gated by Messrs. Schultz and Cross, and the results published 

 in Bulletin 512 of the United States Geological Survey. A 

 brief description of the leucite rocks is given, with an estimate 

 of the amount of potash these rocks m.iy be expected to yield 

 when a suitable process for extraction has been discovered. 

 The latter is now a problem for the technological chemist and 

 the industrial engineer. Several reduction processes for 

 extracting potash from igneous rocks have been patented ; but, 

 so far, none have proved commercially successful. The 

 amount of potash stored in the lavas of the Leucite Hills is 

 estimated at nearly two hundred million tons. 



The mineral alunite, a sulphate of potash and alumina, is 

 also used as a source of potash. An important deposit of this 

 mineral, which promises to afford one source of the much- 

 desired potash, has recently been discovered near Marysvale, 

 Utah. It is described in Bulletin 511 of the United States 

 Geological Survey. The alunite forms a banded vein cutting, 

 at a steep inclination, the volcanic rocks (andesite and dacite) 

 which form the greater part of the Tushar range. It is a 

 fissure filling, not a replacement of the country rock, and has 

 a typical banded or crusted structure. The vein has been 



