The infrared method also allows use of samples consisting of a single grain, a rock chip, or sample from hundreds of feet of drill core. The method does not allow determination of texture which is required to deduce the full pétrographie history of the rock. It will, however, give the present composition of the rock, regardless of the degree of alteration or degree of weathering the sample has undergone. The infrared method is sensitive for minerals formed by alteration or weathering. Pétrographie descriptions of rocks are based on the quantitative determination of quartz content and feldspar types and contents. Based on these fundamental determinations, almost all rocks may be placed in their correct categories. The quantitative determination of black ferromagnesian and other accessory minerals is not essential to classify rocks. At the Kennecott Research Center standard calibration curves are prepared with the infrared spectrophotometer using individual pure minerals. By using synthetic mixtures of minerals, the quantities and types of minerals present in unknowns is determined rapidly. Validity of analytical results obtained in this manner has been checked against the standard granite (G-l) samples distributed by the U. S. Geological Survey. This has been found to be a good sample type to use, as most igneous rocks associated with ore bodies are of this acidic type. The infrared method is insensitive to less common components such as biotite, muscovite, opaque and nonopaque accessories found in the standard granite sample. The technique used involves preparing KBr disks consisting of 2.50 mg. of a preground sample blended into 1.00 gram of KBr and weighing out enough of the blend to form a 12-mm.-diameter disk of the desired thickness. The disks are formed in a vacuum die under 12.5ton pressures. The spectrophotometer used has rock salt optics. The so-called low-cost infrared spectrophotometer can be used in this work.
A Brand New Concept in Molecular
Models
THE GODFREY MOLECULAR MODEL KIT
*
FOR RESEARCH AND PROCESS CHEMISTS, TEACHERS AND STUDENTS Construct all existing organic forms . . . many inorganic forms . . . easily and quickly . . . and with less expense. First to realistically show the flexibility and compressibility of actual atoms using pliable PVC. F E A T U R E S •k
:
Most Accurate Representation of V a n der W a a l ' s a n d Co-valent Radii
k
Correct Presentation of Small Ring Compounds
-k
Clear Demonstration of Hydrogen Bonding, Steric Hindrance a n d Atomic W e i g h t
~k Easy Construction of Bicyclic Compounds k
Atoms M a g n i f i e d 1 6 5 , 0 0 0 , 0 0 0 Times! * U . S. Patent Applied for
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MODEL 40 GODFREY MOLECULAR MODEL KIT Complete in sturdy box with instruction manual, colorful atom models and connectors. Atoms contained: Tetrahedral carbon 17, Trigonal carbon 15, Digona! carbon 5, Hydrogen 32, Digonal oxygen 5, Carbonyl oxygen 5, Quaternary nitrogen 5, Nitrogen amine cap 5, Trigonal nitrogen 5, Chlorine 4, Digonal
