HARD PETROLATUM 329 



marsh-gas series, obtained by distilliDg off the lighter and 

 more volatile portions from petroleum, and purifying the 

 residue when it has reached the desired melting point. 

 When petrolatum is prescribed or ordered without further 

 specification, soft petrolatum is dispensed. 



Properties. — A fat-like mass of about the consistence of 

 an ointment, varying from white to yellowish or yellow ; 

 more or less fluorescent when yellow, especially after being 

 melted ; transparent in thin layers, completely amorphous, 

 and without odor or taste ; or giving off, when heated, a faint 

 odor of petroleum. 



The melting point of soft petrolatum ranges about 40° 

 and 45° C. (104° and 113° F.). In other respects soft petro- 

 latum has the characteristics of liquid peti*olatum. 



3. — Petrolatum Spissum. Hard Petrolatum. (U. 8. P.) 



Derivation. — A mixture of hydrocarbons, chiefly of the 

 marsh-gas series, obtained by distilling off the lighter and 

 more volatile portions from petroleum, and purifying the 

 residue when it has reached the desired melting point. 



Properties. — A fat-like mass of about the consistence of 

 an ointment, varying from white to yellowish or ^^ellow; 

 more or less fluorescent when yellow, especially affer bt^iug 

 melted; transparent in thin layers, completely amorphous, 

 and without odor or taste; or giving off, when heated, a 

 faint odor of petroleum. The melting point of hard petro- 

 latum ranges about 45° and 51° C. (113° and 125° R). In 

 other respects hard petrolatum has the characteristics of 

 liquid petrolatum. 



Action and Uses. — Petrolatum is a valuable emollient. 

 It soothes, protects and softens parts to which it is applied, 

 and is superior to animal and vegetable fats and oils in not 

 becoming rancid, and therefore irritant and malodorous. 

 Petrolatum may be used alone, or as an excipient in the 

 preparation of ointments, but does not aid the absorption of 

 drugs (as do alcohol, glycerin, chloroform, and animal oils 



