In a large bowl stir together salt, cayenne, paprika, and coriander.
In a 4-quart heavy kettle, heat oil over moderate heat until a deep-fat thermometer registers 325 degrees.
While oil is heating, cut potatoes lengthwise into 1/4-inch-thick sticks. Fry potatoes in oil 1 1/2 minutes (potatoes will not be golden) and with a slotted spoon transfer to brown paper or paper towels to drain.
Heat oil to 350 degrees F. Return potatoes to oil and fry until golden and crisp, about 5 minutes. Transfer fries with a slotted spoon to clean brown paper or paper towels to drain and toss fries in spice mixture.