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.
How Many Gallons in a 20 Pound Propane Tank? A 'full' 20 pound propane tank would contain 4.73 gallons of propane. Note that in some US tank exchange programs, the fill is something less than 20 pounds and is labelled accordingly. The image above is a typical 20 pound (9kg) propane tank. Based on the conversion chart above, there are 23.64 gallons in a 100 pound propane tank. A 100 pound tank is roughly the same size as a 45kg gas bottle.