Colour blind

E. Detection of the colour change. With all of the metal ion indicators used in complexometric titrations, detection of the end point of the titration is dependent upon the recognition of a specified change in colour for many observers this can be a difficult task, and for those affected by colour blindness it may be... 

Litmus was probably the most popular choice of acid-base indicator, but it is not a good choice for colour-blind chemists. The use of phenolphthalein as an acid-base indicator comes a close second. Phenolphthalein (XIII) is another weak organic acid. It is not particularly water soluble, so we generally dissolve it in aqueous ethanol. The ethanol explains the pleasant, sweet smell of phenolphthalein solutions. 

Rods absorb maximally at 509 nm, blue-sensitive cones at 420 nm, green-sensitive cones at 530 nm and red-sensitive cones at 565 nm. Colour blindness results from mutations that occur in the genes for the three different colour-sensitive opsin molecules. 

At the heart of much of this book is the fact that human beings are able to see colour by the interaction of light with the receptors in the retina of the eye. Any fault in this mechanism, such as red-green colour blindness, is a distinct hindrance in a world constructed around normal colour vision. 

Adverse effects include optic neuritis, visual disturbance, colour blindness, hyperuricaemia, skin rash, drug fever, malaise, confusion, disorientation, headache, nausea, anorexia, vomiting and abdominal pain. 

The most frequently used tests in quality control in the flavour industry are paired-sample comparison tests, and triangle tests, which are often combined with the description of deviation from a reference item. For the selection and training of panellists, further test methods are used, for example ranking tests for colour, taste and odour, threshold detections (taste, off-flavour), colour blindness tests and odour identification tests [6]. 

Post-ingestion from a-, (3- y-carotene other carotenes from plant leaves a wide variety of fruit, root seed sources e.g. Daucus carota (carrot) (Apiaceae) [root] Retinal covalently linked to opsins (— light receptor Rhodopsins in vision) colour blind John Dalton (atomic theory, 1766-1844) bequeathed his eyes to science 2 centuries on molecular biology confirmed the absence of the gene for the green photoreceptor opsin... 

The use of metal-ion indicators to indicate the end-point of complexometric titrations is based on a specific colour change. Some individuals may find it difficult to detect a particular colour change (e.g. those with colour blindness). Alternative approaches for end-point detection are available based on a colorimeter/spectrophotometer (devices for measuring colour, see Chapter 26) or electrochemical detection (see Chapter 34). 

Colour blindness only affects a fev.reorle in general, but it is said that sore kind of the blindness occurs for everyone if the visual angle of the target is very small i.e. not more than 15. This is the situation when we see an object 4.4 meters wide at a distance of 1000 meters. In this case the eyes resrcnd only... 

A commonly-used device for testing colour perception is the Isihara test. This consists of a number of plates composed of numerous spots of different colours and sizes. Incorporated into this random arrangement are a number of dots, tracing out numerals, which are of a colour distinguishable from the remainder. The colour sensitivity of the observer s eye is assessed by his ability to read these numbers. It is also possible to detect different kinds of colour blindness with the plates. Four of them, for example, each contain two numbers one in scarlet and the other in purple. Those who suffer from panatropy cannot see the scarlet spots and only read the purple ones, but the deuteranopes read only the scarlet numerals those with normal vision see both numbers. (For further information see JORDINSON AND MlNSHALL, J. 5.D.C., 1959, 75, 585.)... 

The ision ])rocess is tlierefore prone to various influences which can affect the perception of detail, briglitness, contrast and colour. Through tests such as those used to examine for colour blindness, the Camouflage Section was able to identify optical illusion-type effects and other methods of visual confusion utilising particular mixes of colours, all of which were incorporated in systems of protective painting for ships. 

Where appropriate, operators should be tested for colour-blindness and the results made known to supervisors under whom they work. 

Within the eye itself there are receptors known as cones which are able to differentiate between the three primary light sources that enter the eye, namely red, green and blue. Where one or more of these receptors is weak, a person will suffer from colour blindness and be unable to distinguish between certain shades. 

The display should be designed such that data can be recognized by operators who may be colour blind. For example, conditions shown by red or green colours could also be shown by filled or unfilled graphics. 

Dalton, John (1766-1844) British chemist and physicist, in 1801 he formulated his law of partial pressures (see Dalton s law), but he is best remembered for Dalton s atomic theory, which he atmounced in 1803. Dalton also studied colour blindness (a condition, once called Daltonism, that he shared with his brother). 

Al-Aqtimi M. T, Al-Qawasmeh M. H. (2001), Prevalence of Colour Blindness in Young Jordanians, Ophthalmologica, 215, 39-42. 

Verhulst S., Maes F. W. (1998), Scotopic vision in colour-blind. Vision Research, 38(21), 3387-90. 

It would have been surprising if F. Reich had not used spectroscopy to prove his assumption. Of course, Reich did use it but, unfortunately, he was colour-blind and, therefore, asked his assistant Richter to perform spectral analysis. 

Systematic errors arise not only from procedures or apparatus they can also arise from human bias. Some chemists suffer from astigmatism or colour-blindness (the latter is more common amongst men than women) which might introduce errors into their readings of instruments and other observations. Many authors have reported various types of number bias, for example a tendency to favour even over odd numbers, or 0 and 5 over other digits, in the reporting of results. It is thus apparent that systematic errors of several kinds are a constant, and often hidden, risk for the analyst, so the most careful steps to minimize them must be considered. 

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