the Manufacture of Artificial Tourmalines. 357 



beam. But although it offers great and manifest advantages 

 when the new tourmalines are crossed at right angles^ yet, upon 

 revolving the superior crystal, and therefore bringing the two 

 plates into a parallel position, we have a blue colour in the field, 

 which must assuredly alter the colours of depolarizing media : it 

 is, however, a very agreeable light to work by, as the intense 

 yellow of gaslight is much mellowed down and counteracted by 

 it. This corrective medium would be inadmissible when the 

 selenite stage is employed, as the tints would be materially 

 changed by its absorptive agency. 



The mode of making this glass is simply to dry powdered 

 biborate of soda in a crucible by the heat of an ordinaiy fire j 

 again reduce the effloresced mass to powder, and mix it with a 

 small quantity of the oxide of copper, such as is generally used 

 in organic analysis ; then introduce the mixture into a platinum 

 crucible, and with a steady, long-continued heat, thoroughly 

 vitrify it, pour it out upon a flat slate, clear metallic or Wedge- 

 wood-ware surface, and press it while still soft into a flattened 

 plate. Upon cooling, a portion must be quickly ground down 

 upon a hone, polished, and then mounted in Canada balsam 

 between glass; the unmounted boracic glass may be kept for 

 any length of time in turpentine without change, but in the air 

 it effloresces, and becomes opake and useless. 



1 have been asked for a process by which the quinine may be 

 recovered from the mother-solutions and from Herapathite itself. 

 The following will be found very successful. 



It is merely necessary to boil the mother-liquids with the 

 Herapathite crystals, add a little solution of some soluble sul- 

 phuret, say potassium or ammonium, to convert the iodine into 

 hydriodic acid, evaporate to dryness so as to expel the spirit, 

 acetic acid, by a water-bath ; redissolve the remaining salt in 

 just sufficient boiling distilled water, filter, and set aside to cry- 

 stallize ; filter when cold, and dry the crystals by expression, and 

 by a gentle heat. 



The mother-liquid contains acetate and some sulphate of 

 quinine; add to it, when cold, an alkali in solution, potassa, 

 soda, or ammonia, or the carbonates of these ; collect the sepa- 

 rated alkaloid on a filter, and dissolve it in boiling water acidu- 

 lated with sulphuric acid; if this be not in excess, the disulphate 

 of quinine crystallizes on cooling, and the loss is very slight*. 



32 Old Market Street, Bristol. 



* This disulphate may be again employed for the manufacture of the 

 crystals ; so may the neutral sulphate of quinine obtained by the first part 

 of the process. 



