458 JOURNAL OF THE SOCIETY OF COSMETIC CHEMISTS ::! ..... Figure 5 (A & B).--65% ethyl alcohol, 35% propellant 12. Valve "C" break-up spray actuator. continue without interruption into the large external orifices. A product utilizing a foam actuator will yield a foam immediately after discharge from the external orifice. The nature of the foam is affected primarily by the type and amount of the propellant. The varying types of foam produced by the different propellants may, in part, be related to the vapor pressure of the propellants used in the formulation. Thus different propellants present in the same concentrations will yield different foams, those with higher pressures tending to give stiffer and more elastic foams than those with lower pressures. With any given propellant stiff, dry and elastic foams are produced at higher propellant concentration, whereas soft, somewhat wet and less resilient foams are produced at lower pro- pellant concentrations. Foams are assessed by determining the density, the overrun and possibly also by "feel." Foam density may be determined by discharging into a vessel of known volume and tare, and weighing the amount contained therein. It is best to discharge an equal quantity to waste, prior to the actual determination to ensure that possible spout residues do not influence the result. The per cent o/overrun indicates the volume of t•)am that is produced and is defined as

SPRAY PATTERNS OI: COSMETIC PRESSURE PACKS 459 volume of foam -- volume of liquid X 100 % overrt, n = volume of liquid It depends primarily on the concentration of propellant, and the nature of the aqueous formulations. It is •vorthwhile mentioning that a spray which gives a foam on im- pingement may be obtained when using a standard spray actuator rather than a foam actuator. This method of dispensing is often resorted to when using glass packs as very few foam actuators are suitable for use with 20 min., or thereabouts, valve closures. •.. -•..- •.•. :•--• •.• • .... . ..,/•..•., ... - ,•,, -•.' •-i•-.:...'•t5.-% ' ' • .... -.,.. •-• ?•.i•,•:•?{.,..• ..•,...,.•,.• ß • ...... .• .• .... 5.•.-:a• •x•, a • '",:•: '• ß •-2 ' •'• •' .... 'S.•S...a • .. '•' - :•'•}• .. •2. :. "'•'. " .... c•'• %.. •-•, -.,.,•.- • •.•% • •:.• -.:7- ß ...... • .... " S:..•: "•.': ' a-,•.• gi• ..... •. •. ..•..... :.• •.'• ß ' •. • Figure 6 (A & B).--66% ethyl alcohol, nitrogen at 90 p.s.i.g. Valve "A" break-up spray actuator. For streams the special actuators developed principally for nitrogen packs must be employed and correct discharge is primarily a function of the product itself, once it has been established that the viscosity is not too high for discharge through the selected valve. Propellant pressure merely controls the proportion of the original fill that will ultimately be discharged, i.e., the amount of undischargeable product. Thus once the valve has been