15 15 benzyl alcohol 5 5 5 5 5 5 water 75 75 75 75 75 75 the numbers are by weight 0019 table 3 composition of examples example nos 13 14 15 16 17 18 lanthanum chloride heptahydrate 2 u2014 u2014 u2014 u2014 u2014 gadolinium acetate tetrahydrae u2014 u2014 u2014 u2014 2 u2014 samarium chloride hexahydrate 2 u2014 u2014 u2014 2 u2014 dysprosium chloride hexahydrate u2014 2 u2014 u2014 u2014 u2014 holmium chloridehexahydrate u2014 u2014 2 u2014 u2014 u2014 ytterbium chloride hexahydrate u2014 u2014 u2014 2 u2014 u2014 lactic acid u2014 u2014 u2014 u2014 u2014 2 polyacrylic acid 1 1 1 1 1 1 ethanol 15 15 15 15 15 15 water 5 5 5 5 5 5 the numbers are by weight to provide for the experiments below the reference compositions were prepared by mixing the components described in table 4 these reference compositions contain salts except rare earth metal salts or an acid 0021 table 4 composition of references reference example nos 1 2 3 4 5 6 zinc chloride 2 u2014 u2014 u2014 u2014 u2014 bismuth chloride u2014 2 u2014 u2014 u2014 u2014 lithium chloride u2014 u2014 2 u2014 u2014 u2014 indium chloride tetrahydrate u2014 u2014 u2014 2 u2014 u2014 magnesium chloride hexahydrate u2014 u2014 u2014 u2014 2 u2014 callic acid u2014 u2014 u2014 u2014 u2014 3 lactic acid 2 2 2 2 2 u2014 ethanol 15 15 15 15 15 15 benzyl alcohol 5 5 5 5 5 u2014 water 76 76 76 76 76 82 the numbers are by weight approximately 0 03 gram of standard house dust contains approximately 1000 micrograms gram of mite der 2 allergen was rubbed over the felt 6 6 cm in diameter and the compositions 1 to 18 and reference.