Fall colors

Other interference-produced colors falling into this section include doubly refracting materials such as anisotropic crystals and strained isotropic media between polarizers, as in photoelastic stress analysis and in the petrological microscope. 

The stibmlphide is the cethiops mineral of the older chemists, and was prepared by agitating a little water, sulphur, and mercury, in equal proportions, in a mortar, or at a slightly increased heat, till a black powder resulted.. It oan bo obtained by transmitting a stream of sulphide of hydrogen ges through a dilute solution of subnitrate of mercury in the cold, when a subsulphide of a black color falls. The reaction is as follows... 

In a small mortar grind 2 g of green or brightly colored fall leaves (don t use ivy or waxy leaves) with 10 mL of ethanol, pour off the ethanol, which serves to break up and dehydrate the plant cells, and grind the leaves successively with three 1-mL portions of dichloromethane that are decanted or withdrawn with a Pasteur pipette and placed in a test tube. The pigments of interest cU e extracted by the dichloromethane. Alternatively, place 0.5 g of carrot paste (baby food) or tomato paste in a test tube, stir and shake the paste with 3 mL of ethanol until the paste has a somewhat dry or fluffy appecu-ance, remove the ethanol, and extract the dehydrated paste with three 1-mL portions of dichloromethane. Stir and shake the plant material with the solvent in order to extract as much of the pigments as possible. 

Before windsurfing became a big hit, Hood River was famous among epicureans for its orchards and vineyards. The area s fruits are coveted by gourmet chefs worldwide. In the autumn, take a drive down the Mt. Hood Loop tour and stop at any of the fruit stands along the way. Another way to enjoy the local bounty is to visit the Hood River Harvest Festival held in mid-October. Pick up locally grown winter pears, Bartletts, Newton apples, cherries and peaches amid a backdrop of colorful fall foliage. Admission to the festival is free. 

Boundary-line colors refers to colors falling between the major categories of clear, pale yellow, yellow, and amber. In other words, pale yellow to one observer is obviously yellow to another, even when each person is being as objective as possible. The problem is not unique to cement microsco-pists. An attempt at a photographic belite color standard is presented in this book. 

The Meteor and Meteor Plus colorants fall into two main classes of stable crystal structures spinels and rutiles. 

In the process of testing, color deviations are expressed ia the CIELAB system which projects total color differences either on the axes of the rectangular LAB or the equivalent polar LHC system (26). In either case tested samples must fall within acceptable ranges or limits estabhshed versus a standard by the pigment manufacturer and accepted by the pigment user. 

Drying of the poly(vinyl alcohol) is critical to both the color and solubiHty of the final product. Excessive drying temperatures result in high product color and an increase in the crystallinity, which in turn reduces the solubiHty of the product. Drying is initially subjected to a flash regime, where the solvent not contained within the particles is flashed off. This first phase is foUowed by a period where the rate is controUed by the diffusion rate of solvent from the poly(vinyl alcohol) particles. Because the diffusion rate falls as the material dries, complete drying is not practical. The polymer is therefore generally sold at a specification of 95% soHds. 

When considering light of a certain spectral energy distribution falling on an object with a given spectral reflectance and perceived by an eye with its own spectral response, to obtain the perceived color stimulus it is necessary to multiply these factors together as ia Eigure 6. Standards are clearly required for both the observer and the illuminant. 

The colors obtained depend primarily on the oxidation state and coordination number of the coloring ion (3). Table 1 Hsts the solution colors of several ions in glass. AH of these ions are transition metals some rare-earth ions show similar effects. The electronic transitions within the partially filled d andy shells of these ions are of such frequency that they fall in that narrow band of frequencies from 400 to 700 nm, which constitutes the visible spectmm (4). Hence, they are suitable for producing color (qv). 

In milk approximately 90% of the yellow color is because of the presence of -carotene, a fat-soluble carotenoid extracted from feed by cows. Summer milk is more yellow than winter milk because cows grazing on lush green pastures in the spring and summer months consume much higher levels of carotenoids than do cows ham-fed on hay and grain in the fall and winter. Various breeds of cows and even individual animals differ in the efficiency with which they extract -carotene from feed and in the degree to which they convert it into colorless vitamin A. The differences in the color of milk are more obvious in products made from milk fat, since here the yellow color is concentrated. Thus, unless standardized through the addition of colorant, products like butter and cheese show a wide variation in shade and in many cases appear unsatisfactory to the consumer. 

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