187 



April 1915, a number of specimens of P. communis var. bovis were 

 received, Sarcoptes scabiei var. bovis being also present. These are 

 believed to be the only records of P. communis var. bovis having been 

 found in South Africa. P. communis var. cuniculi is very common in 

 the ears of domestic rabbits in South Africa. Attempts made to 

 transmit this mite to horses, calves and sheep were unsuccessful. 



Green (H. H.). The Sulphur Sheep Dips. — Union S. Africa, Dept. 

 Agric, Pretoria, 3rd & 4th Repts. Director Veterinary Research, 

 November 1915, pp. 115-156, 3 plates. [Received 12th October 

 1916.] 



The author's summary of this paper on the chemistry of the sulphide 

 dip is as follows : — 



1. The caustic soda and sulphur dip, as prepared according to the 

 recommendation of the Division of Sheep, consists of a mixture of 

 sodium pentasulphide and sodium thiosulphate with a distribution of 

 sulphur about four-fifths of the former and one-fifth of the latter. 

 No monosulphide can be detected and only traces of sulphate are 

 present. There is even the suggestion that polysulphides higher than 

 the pentasulphide exist for a short time in the freshly prepared dip. 

 The proportions of caustic soda and sulphur actually going into 

 combination are approximately five to eight, and the recommended 

 formula, 5, 20, 2|-100, provides so large an excess of free sulphur that 

 complete utilisation of caustic soda is ensured even under somewhat 

 careless conditions of dip-making. The presence of free caustic soda 

 in the dip need not therefore be feared if the instructions for dip-making 

 are carefully carried out. The preliminary mixing of the svilphur to a 

 homogeneous cream with water is the most important step to be 

 observed, since it is upon the intimacy of subsequent contact of the 

 sulphur Vv^ith the caustic soda solution that, the reaction mainly depends. 

 Combination takes place at comparatively low temperature, and may 

 be completed in forty minutes at 50° C, although reaction is of course 

 more rapid at higher temperatures. If hot water is used in the pre- 

 liminary mixing, the heat evolved as the caustic soda is sprinkled in 

 suffices to keep the mixture near the boiling point, and boiling by the 

 application of external heat is therefore unnecessarv. Boiling, 

 however, may offer slight advantages in completing the reaction in 

 cases where the preliminary process has been imperfectly carried out. 

 With ordinary care a dip of correct composition always results, without 

 boiling. If the sulphur is not properl}' wetted in the preliminary 

 mixing to a cream, the bulk of it may float on the surface and cake 

 as the caustic soda is sprinl^led in, and so partly escape combination. 

 The dip may then contain residual free aikah, but not, as might be 

 expected, any appreciable amount of sodium monosulphide. 



2. The lime-sulphur dip is analogous in composition to that of the 

 caustic soda and sulphur clip, and consists of a mixture of calcium 

 pentasulphide with calcium thiosulphate. In preparing the dip the 

 ingredients must be boiled and the so-called " raw lime-sulphur dip " 

 consists of a mixture of hme and sulphur. At least two parts of sulphur 

 to one part of unslaked lime should be used whenever a reallv good 

 sample of lime is available. If other proportions are used, the material 

 present in smaller amount determines the solution of the other ; higher 



