Christian Missions in Persia. Christianity was introduced in Persia in the Parthian period, and several bishoprics were established there (Latourette, II, pp. 263ff.).
You will likely pay more for the exchange, even if your tank is completely empty. An empty 20 lb tank will hold about 4.7 gallons of propane. That is $18.47 at $3.93 per gallon, which is the low quantity price (I just paid $3.44 per gallon when filling several tanks). The exchange is about the same price. Keep in mind this comparison is as if the exchange gives you a FULL tank.
tank on a grill. With propane weighing 4.4 pounds per gallon, the reference of the size of the cylinder determines the volume. Example of the 20 pound LPG cylinder on the grill will provide approximately 4.5 gallons of liquid propane. A 100 pound cylinder will provide approximately 20 gallons of liquid propane.