Odour recognition thresholds were determined for; ethylamine, diethylamine, triethylamine, n-butylamine, di-n-butylamine, tri-n-butylamine, pyridine and n-butanol. Quality descriptions, intensity and hedonic ratings over a range of concentrations were also determined for these compounds. All measurements were made with an air dilution olfactometer. Considerable differences between the thresholds of amines were found, but these appeared to vary systematically only within the butylamine series. No odour changed markedly in quality over the concentration ranges presented. However in contrast to the ethylamines and n-butylamine which are ‘ammoniacal’, the major quality of di- and tri-nbutylamine was described as ‘sweet’. Changes in odour intensity and pleasantness were assessed using the method of magnitude estimation with n-butanol as the reference odorant. The relationship between perceived intensity and concentration for each odorant was best described by the power function log I = log k + n log C. The value of the exponent n (slope) ranged from 0.46 (pyridine) to 1.31 (ethylamine). Four odorants, namely ethylamine, diethylamine, n-butylamine and tri-n-butylamine had an exponent < 1. These are the first examples of odorants whose exponents exceed unity. Pleasantness ratings for all compounds fitted a quadratic function Log p = k1 + k2log C + k3(log C)2 and were therefore not reciprocals of intensity scores. The pleasantness of most of the odorants decreased as the concentration was increased from the threshold level.
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Laing et al. (1978) studied this question.