Several methods other than colorimetric, are available for the determination of sterols. These methods may be summarised, in ascending order of sensitivity, as follows: gravimetric, involving the precipitation of 3-P-hydroxy steroids with digitonin (W i n d a u s , 1910; L i n f o r d , 1956; H a u s t et al., 1966; V a h o u n y et al., 1960); flourometric (A1 b e r s and L o w r y , 1955); gas liquid chromatographic for cholesterol (B 1 o o m f i e 1 d , 1962; S c h m i d t and M a t h e r 1964; W i l-Cowley et al., Sterols in Digitalis Bd. 19, Heft 3 Plant Material Seeds of D.prrrpurea were obtained from Verenigde Nederlandse Kruidencooperatie G. A., Elburg, Holland. The leaves were obtained from mature second year plants grown from seed. Chemicals The reference sterols p-sitosterol and ergosterol, were obtained from R. N. Emanuel Ltd., and stigmasterol from Koch Light Ltd. The compounds were purified by thin layer chromatography on 1 mm layers of silica gel G activated a t 120° C for 45 rnin, and developed wth chloroform: methanol (99 : 1). They were recovered by elution with chloroform and recrystallised from acetone. W e are grateful to Dr. B a i s e d for a sample of campesterol. Reagents Solutions of the purified sterols, Tables I-IV, were made up in glacial acetic acid and stored at 25' C for 30 rnin prior to use. The colour reagent, acetic anhydride containing 5% of sulphuric acid, was also kept for 30 rnin a t 2. 5' C before use, and was not used after 40 min, from the time of preparation. The acids and the acetic anhydride were of analytical reagent grade.
Mineral insulated, metal sheathed (MI) Type K and Type N thermocouples are widely used in industry for process monitoring and control. One factor that limits their accuracy is the dramatic decrease in the insulation resistance at temperatures above about 600 °C which results in temperature measurement errors due to electrical shunting. In this work the insulation resistance of a cohort of representative MI thermocouples was characterised at temperatures up to 1160 °C, with simultaneous measurements of the error in indicated temperature by in situ comparison with a reference Type R thermocouple. Intriguingly, there appears to be a systematic relationship between the insulation resistance and the error in the indicated temperature. At a given temperature, as the insulation resistance decreases, there is a corresponding increasingly negative error in the temperature measurement. Although the measurements have a relatively large uncertainty (up to about 1 °C in temperature error and up to about 10 % in insulation resistance measurement), the trend is apparent at all temperatures above 600 °C, which suggests that it is real. Furthermore, the correlation disappears at temperatures below about 600 °C, which is consistent with the well-established diminution of insulation resistance breakdown effects below that temperature. This raises the intriguing possibility of using the as-new MI thermocouple calibration as an indicator of insulation resistance breakdown: large deviations of the electromotive force (emf) in the negative direction could indicate a correspondingly low insulation resistance.
T h e phytosterols of Digitalis purpurea L. can be separated into a polar glucoside fraction, and a non-polar lipid fraction. (C o w l e y, E v a n s and G i n m a n 1971). The glucoside fraction consisted of the normal 5-ene phytosterols as reported earlier by J a c o b s o h n and F r e y (1967). The lipid fraction was more complicated, consisting of 7-ene and 5-ene sterols, together with C-4 methylated compounds. (E v a n s 1972). This communication describes an investigation into the variations in amounts and relative proportions of glucoside and lipid 5-ene phytosterols of D. purpurea during germination of the seeds. Experimental Plant Material: The seeds were obtained from Verenigde Nederlanse Knuidencoopertie. Germination of Seeds: The seeds were evenly spread on sheets of blotting paper. These were placed on beds of moist, sterile sand and peat mixtures. After an initial spraying the seeds were watered by wetting the support media. Every fourth day the beds were sprayed with a copper fungicide, and every seventh day a nutrient solution was given. (M e d o r a et al., 1967). Germination took place in a glass house under natural conditions of light and darkness at an average temperature of 25" C. The seedlings were collected by scraping the paper sheets and weighing at once to obtain the fresh weight. Reagents: All reagents were of analytical grade. Apparatus: Colorimetric analysis was carried out with a Hilgar and Watts ,UV' spectrometer at 25" C + 1. Gas-liquid chromatographic traces were obtained on either a Marryat GLC unit fitted with 9' X ' I," glass column (Chromosorb W. (100-120), 1.5% SE. 30) (Column I), or on a Pye 104 fitted with a 13' X '/4" glass column packed with similar material (Column 2). Extraction and Colorimetric Analysis: The seeds and seedlings were homogenised, extracted and analysed calorimetrically as previously described. (C o w l e y et al. 1971). From the remaining neutralised solutions the sterols were recovered with dichloromethane. Gas-Liquid Chromatographic Analysis 1. Glucoside Sterols: The acetates were prepared (pyridinelacetic acid (111)) and purified by preparative layer chromatography (PLC) on 500 p layers of silica gel H previously activated at
The morphology and detailed anatomy of the inflorescence of Digitalis purpurea have been described. The diagnostic characters which are the most valuable in identifying the inflorescence are the glandular trichomes, which are present on most parts; the pollen grains; the striated cuticle of the calyx and pedicel; the pericyclic fibres of the calyx, pedicel and stem, also the lignified cells of the anther, fruit wall and seed coat.
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