48 THE MICROSCOPE 



then soaking for 24 hours in enough distilled water to cover the 

 gelatine ; heating this gently over a water-bath, and filter 

 through clean white flannel ; this should be done each time the 

 injection mass is prepared) in a porcelain jar. In a second jar 

 mix 2 parts of b with 4 parts of the gelatine mixture. Carefully 

 mix these two gelatine masses at a temperature of from 25''. — 

 32^ C, stirring rapidly with a glass rod ; then heat in a water- 

 bath to about from 70° to 100° C. for an hour, and filter through 

 flannel. In order to prevent the formation of a sediment, a 

 further heating and filtering may be necessary. (Frey.) 



Thiersch's Prussian Blue with Oxalic Acid.— Prepare a cold 

 saturated solution of the sulphate of the protoxide of iron {a), a 

 similar one of ferrocyanide of potassium — that is, prussiate of 

 potash ip) ; and thirdly, a saturated solution of oxalic acid {c) ; 

 finally, a warm concentrated solution (2 to i) of fine gelatine. 

 About \ ounce of the gelatine solution is to be mixed in a 

 porcelain dish, with 6 c.cm. of the solution a. In a second 

 larger dish, i ounce of the gelatine solution is to be combined 

 with 12 c.cm. of b, to which 12 c.cm. of the oxalic acid solution c 

 is afterwards added. When the mixtures in both dishes have 

 cooled to about 25° or 32° C, the contents of the first dish is to 

 be added dropwise, and with constant stirring, to the mixture in 

 the latter. After complete precipitation, the deep blue mixture 

 which is formed is to be heated to 70^ or 100^ C. for a time, and 

 constantly stirred ; finally, it is to be filtered through flannel. The 

 injecting fluid thus obtained keeps well in Canada balsam. The 

 depth of its colour niay be readily modified to any desired degree 

 by adding a larger quantity of the gelatine solution. (Frey.) 



Seiler's Carmine Gelatine.— (a) Best carmine, 2 drachms; 

 distilled water, 3 ounces ; strong liquor ammonia, 20 drops. 

 Dissolve this and filter, covering the funnel with a piece of glass 

 plate to prevent the evaporation of the ammonia. (b) Cox's 

 gelatine, 2 drachms ; distilled water, 2 ounces. Soak the gelatine 

 until soft, then dissolve it in a water-bath, and strain through fine 

 flannel while hot. Heat the gelatine solution again, and add the 

 carmine solution. Bring the temperature up to 100° F., and add 

 dilute acetic acid, drop by drop, under constant stirring, until the 



