328 Mr. Donovan on the [Nor. 



the temperature of about 350°, for two hours, continually stirring 

 them. At the end of the process, it appeared that every ounce 

 of lard had dissolved and united with 21 gr. of oxide. 



I tried the effects of this ointment on several persons, and 

 found it to be as active as the common mercurial which contains 

 almost twelve times more mercury. One drachm could be rufo- 

 bed in completely in from 6 to 10, or 15 minutes ; while an 

 equal quantity of common ointment will require 30 or 40 minutes. 

 This to debilitated persons is a great advantage, the usual mode 

 of friction being to such patients a most laborious undertaking. 

 In but one or two cases, was any eruption produced on the part 

 rubbed, and this was inconsiderable ; but in the common mode, 

 the pustules are often so painful and numerous as to preclude the 

 further continuance of friction. The use of the new ointment is 

 extremely cleanly, the parts being left scarcely discoloured ; and 

 this, when privacy is an object, is of great importance. The last 

 advantage, and to the hospitals not an inconsiderable one, is the 

 comparative cheapness of the new ointment : the common mei> 

 curial ointment costs in Dublin from 4s. to 5s. a pound ; the 

 other can be prepared at an expense little above that of the lard. 



For the preparation of this ointment, it is essential that the 

 lard be entirely free from salt ; if not, calomel will be formed. 



The oxide may be prepared by decomposing calomel with 

 solution of pure potash ; or, which is cheaper, by pouring solu- 

 tion of nitrate of mercury into caustic alkaline solution. 



Although the fat will scarcely dissolve more than 3 gr. of 

 oxide to each drachm, the quantity of oxide may be more if 

 necessary. The ointment that I employed was merely satu- 

 rated. The oxide should be first triturated with a little lard in 

 the cold, to make the penetration complete. 



The degree of heat at which the combination is attempted is 

 material. At 212° the oxide and lard will not combine ; at 600° 

 the oxide will be decomposed, and mercury volatilized ; at 500 9 

 and 400°, the oxide is partially decomposed, some red oxide 

 being formed, and mercury reduced. The best heat is between 

 300° and 320°; it should be maintained at least an hour, and the 

 ointment should be stirred till cold. 



An ointment composed of what has been called ash-coloured 

 oxide of mercury mixed with lard was formerly in use ; but was 

 found not to answer the purpose. The reason is plain. The 

 oxide contained a mercurial salt, not soluble in fat; and the 

 oxide was not combined, but mixed in the ointment. 



Whether the cure effected by this ointment be permanent, 

 experience alone can decide. I see no reason for the contrary 

 opinion. It contains as much oxidized mercury, in a state of 

 combination, as the common ointment ; the metallic mercury in 

 the latter being not only useless, but hurtful, by obstructing the 

 absorbents, and thus retarding the entrance of the oxide into the ciiv 

 culation, and by exciting a diseased action in the surface rubbed; 



