Identification Stain for Chrysotile Asbestos

THE use of organic and inorganic stains has found wide application as a means of detection and estimation of organic fibres. Such stains have enabled the analyst to distinguish between organic fibres of different type and even between wood fibres produced by different processes. Among these stains, aqueous iodine solutions have figured prominently, as in the case of the well-known Sutermeister and Herzberg stains. At the Johns-Manville laboratories, the idea of applying a stain to asbestos fibres was first considered solely as a visual aid in the microscopic examination of such fibres. The staining medium used in this work consisted of a 1 per cent solution of iodine in C.P. glycerine, the latter being used extensively here as a dispersing and mounting liquid for asbestos fibre. This iodine solution was found to have distinct staining properties when used on the local chrysotile fibres, and to improve greatly their visibility under the microscope. It was soon revealed, however, that this staining is apparently limited to the chrysotile variety of asbestos, as against other varieties. It can be readily seen that, if such were the case, the staining test would become a very useful tool in differentiating between chrysotile fibre and the other mineral fibres, without recourse to a lengthy chemical analysis. Hence this investigation was launched, with the purpose of obtaining more information as to the selectivity of this stain as well as its mechanism. The only previous work of this nature that could be found in the literature was that of Van Winsen and Graham (1, 2, 3) on the adsorption of erioviolet dye by serpentine and related magnesia minerals. However, these authors did not refer to any specific behaviour of chrysotile as against other types of asbestos fibre.