The purchaser may record the certificate of sale in the office of the clerk or register of deeds of the county in which the land is situate, as a mortgage of land. The register or county clerk, as the case may be, shall index the certificate in his index of mortgages in the name of the delinquent owner, as set forth in the certificate, and shall also index it in a separate block index, to be kept in his office, under the block and lot number as shown in the certificate, if the property is described by lot and block.