摘要:

The known methods for detecting the presence of tyroglyphids are described. For coarse materials, such as seeds, sieving is recommended. For flour, it is better to examine exposed surfaces, or to keep samples in glass vessels and examine for the runnels made by mites against the glass. Methods of sampling to provide information about the density and extent of infestations are described. Samples must usually be treated in the laboratory. While methods which do not involve the separation of the mites from the material are referred to, such separation is usually necessary. Mites may be separated from most materials by the modified Berlese funnel method of Chernuishev and Petrova; means of overcoming certain disadvantages are suggested. However, vigorous sieving is recommended for coarse materials, and a flotation method, using dichlorethylene, for fine materials such as flour. It is usually more satisfactory to examine and count the mites than to estimate the numbers volumetrically or gravimetrically. They are counted in a dish containing oil, placed on squared paper under a low‐power microscope. A modification of this method, for dealing with large numbers, is described. Methods of expressing population density are briefly discusse

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06762.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

To meet the need for a simple method of measuring humidity in small spaces, a new method of using paper impregnated with cobaltous salts has been developed. Cobalt chloride paper is blue at low and pale red at high humidities, with a series of lilac colours between. There is a close correspondence between colour and relative humidity, although the colour is influenced slightly by temperature. It is shown that the colour is determined chiefly by the relative quantities of cobalt chloride and water in the paper. The paper is impregnated by dipping in a solution of CoCl2.6H2,O. The time required for a piece of CoCl2, paper to reach equilibrium with the atmosphere depends chiefly on humidity and temperature; up to 2 hr. exposure is allowed. Colour standards for the matching of test papers are prepared by exposing papers over constant humidity solutions and then sealing them up in liquid paraffin between opal and clear glass. It is possible to measure humidities from 40 to 70% R.H. to the nearest 2% R.H., and above this range to the nearest 5%, except for low humidities at low temperatures.Various colloid substrates other than paper, including mercerized cotton, cause the blue colour to persist at somewhat higher humidities; possible uses of this are suggested. Certain salts, such as potassium thiocyanate and sodium thiosulphate, produce a similar, but much greater effect, and also produce stronger colours. The method can thus be adapted for accurate use at higher humidities. Alternatively, the addition of zinc chloride or certain other salts adapts the method for use at low humidities.Papers more suitable for use at high humidities have been prepared with cobalt thiocyanate solution. A further improvement is the use of pure cotton tissue paper. Methods of impregnating the paper are described, also the above‐mentioned method of preparing standards. Approximate corrections for temperature are given. The influence of temperature and humidity on the time taken to reach colour equilibrium is described. An exposure of 30 min. is sufficient except at very high humidities, where up to 2 hr. may be necessary. Corrections are given for use when exposures other than 30 min. are allowed. The standards cover humidities above 50% R.H. at intervals of 5% R‐H.; teat papers can be estimated to about the nearest 1% R.H. But under unfavourable conditions, errors may amount to as much as ± 5% R.H., unless the corrections are

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06763.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

摘要:

List of Corronon British Plant Diseases. Compiled by tbe Plant Pathology Committee of the British Mycological Society.Plant Viruses and Virus Diseases. By F. C. BAWDEN.

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06764.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY

ISSN:0003-4746    

DOI:10.1111/j.1744-7348.1945.tb06765.x

出版商:Blackwell Publishing Ltd    

年代:1945

数据来源: WILEY